The first issue to look at is what is meant by manuscript. A manuscript is simply a handwritten copy of the New Testament dating to before the invention of the printing press (mid 1400s). These could be copies of the entire New Testament (NT), portions of it (such as just the Gospels or just the epistles of Paul) or simply fragments of a book of the NT. They are of several types: 

PAPYRI: 
The earliest manuscripts are know as papyri. They are so called because they were written on papyrus. This material was produced from the papyrus plant. Strips of the plant were laid beside and on top of another, moistened and pressed together and cut into the desired size. Generally, these sheets were then arranged into scrolls. But the early Christians, instead, folded them down the center and bound them together into what is known as a "codex."  To date, 88 papyri have been cataloged. These date from the second to the eighth centuries. 41 are from the second to the fourth centuries. The earliest is a fragment of the Gospel of John and dates to about 125 C.E. The fragment contains John 18:31-33,37,38. It is now on display at the John Rylands Library in Manchester. The papyri are cataloged in scholarly works by a fancy looking "p" and a superscript number. The John Rylands fragment is number 52.  In the fourth century, parchment began to be used. This was made from animal hide. The hair and flesh were removed and the hide trimmed to size, polished and smoothed with chalk and pumice stone. Parchment was used until paper became popular in the twelfth century. 

UNCIALS: 
The uncials are the first kind of manuscript written on parchments. They are so called because the entire text was written in capital Greek letters. About 290 uncials have been recognized. They date from the fourth to the fifteenth centuries. The two earliest are "Codex Sinaiticus" and "Codex Vaticanus." They are named after monasteries on Mount Sinai and in the Vatican, respectively. Both date from the early fourth century. These are also the earliest complete copies of the Bible known. They are also known as, "Aleph" (the first letter of the Hebrew alphabet) and "Beta" (the second letter of the Greek alphabet), respectively.  They are designated with successive English capital letters and a number, with a "0" as the first digit. For instance, "Beta" is designated by B 03. The next earliest uncial is "Codex Alexandria" from the fifth century and is designated as "A 02." The only exception is "Aleph" which uses the Hebrew letter "Aleph" instead of an English letter. 

MINUSCULES: 
The next kind of manuscripts are the minuscules. They are so named since they are written in small letters, with capitals only used as in modern day writing. These are also called "cursives" (running) because they are written in running script. The minuscules date from the ninth to the fifteenth centuries. The earliest is from the year 835 and is located in the Leningrad Public Library. There are about 2,800 know minuscules. They are simply numbered consecutively. In addition to actual texts of the Greek NT, there are three additional sources to be consulted in textual criticism. 

LECTIONARIES: 
The first additional source are the lectionaries. These contain portions of Scriptures that have been divided up into readings for church services. There are approximately 2,200 known lectionaries. They date from the ninth to the fifteenth centuries and are designated by a fancy "l" with a superscript number. 

PATRISTIC CITATIONS: 
The second additional source are patristic citations. These are quotes of the NT in commentaries and other writings of the Church Fathers (church leaders during the centuries immediately following the Apostles). The use of these in textual criticism can be difficult since it cannot always be determined if the writer was copying the Biblical quote directly from a text, quoting it from memory or simply making an allusion to a Scripture verse.  There are dozens of Church Father's which can be appealed to. Some of the more important are: Clement of Rome (c. 95), Ignatius (d. 117), Tertullian (c. 160-220), Origen (185-254), Clement of Alexandria (before 215), Hyppolytus (d. 235), Irenaeus (c. 250), Ambrose (c. 340-397), Chrysostom (344-407), and Augustine (354-430). Various abbreviations are used to designate these and other Patristic citations. 

EARLY VERSIONS: 
The last additional source are the early versions. These are translations of the Greek NT into other languages. The most important of these are the early Latin versions. The NT was probably first translated into Latin around 200 C.E. The earliest manuscript of such a version is from the fourth century. 50 manuscripts have been categorized. They are designated by "it" (for Itala) with a letter superscript.  Next in importance is the Vulgate. This Latin translation was the work, at least in part, of Jerome (c.345-420). It became the official version of the Roman Catholic Church. This accounts for the over 8,000 copies which exist. The earliest is from the fourth century. These are designated by "Vg" and a letter superscript.  Other languages into which the NT was translated in the early centuries are: Syriac, Coptic, Armenian, Georgian, Ethiopic, Gothic, Arabic and many others. Various abbreviations are used for each language (above information taken from Aland, Text, 56,57,75-217, Barker, 53-57 and charts in the UBS text). 

So there are thousands of manuscripts from which to determine the text of the NT from. Out of these, over 85% of the text found in ALL manuscripts is identical. So again, the text of the NT is very well attested. However, this still leaves about 15% of the text in which there are variants between the manuscripts. When these variants are compared it becomes apparent that the manuscripts divide into at least two "families." 

The most important differences can be seen between textual families, although there are still minor variants between manuscripts within a particular text-type. The first of these textual families is the "Byzantine." It is so named since this is the type of text the Byzantine (Eastern, Greek-speaking) church has used throughout its existence.  Byzantine type texts comprise the vast majority of the manuscripts. Most of the above mentioned uncials, minuscules and versions reflect this text-type. These manuscripts are generally "late" (i.e. dating after the fourth century). But some are earlier and a few papyri are also classified here.  The second major textual family is the "Alexandrian" (named after the Egyptian city). Only a handful of manuscripts reflect this type, but most of these are "early" (i.e. the fourth century or before). The above mentioned Codex Sinaiticus and Codex Vaticanus reflect this type, along with some of the papyri. Two less important text-types are the "Western" and the "Caesarean." There is disagreements among scholars on whether these even constitute separate families. 

There is heated debate as to which of the above two major textual families best reflects the autographs (the original texts actually written by the apostles). And this disagreement has led to the development of two different Greek texts for which to translated the NT from. The first is the "Majority Text" (MT). It is so named since it is developed with the assumption that, under God's providence, the best reading was preserved in the MAJORITY of the manuscripts. With this principle, the MT inevitably reflects the Byzantine text-type. 

The "Textus Receptus" (TR) is very similar to the MT. This was the Greek text the monumental King James Version of 1611 was translated from. More recently, the New King James Version was translated from the TR. Two lesser known modern-day versions are also based on a TR/ MT type text. These are the Literal Translation of the Bible and the Modern King James Version. 

The other modern-day, Greek text is called the "Critical Text" (CT) since it is developed by textual CRITICS. The principles underlying this text were first put forth by B.F. Westcott and F.A. Hort in the late 1800s. These principles include the idea that the text of the NT should be approached like any other ancient book.  As such, according to Westcott and Hort, manuscripts should be "weighed not counted." One major consideration in "weighing" a manuscript is its age, the earlier the better. Given this principle, their Greek text mainly reflected the Alexandrian text-type. The "Revised Version" of 1881 was based on this kind of Greek text. 

Today, the 26th edition of the Nestle/ Aland Greek text and the third edition of the United Bible Societies text are similar to the Westcott and Hort text.  The books containing each of these texts also contain extensive charts and apparatus for doing textual studies. Whenever textual variants occur, the apparatus at the bottom of the page indicates which manuscripts have which reading by the use of the above mentioned symbols. The charts provide information about the dates and contents of the various manuscripts referred to. In the footnotes generally all of the Alexandrian manuscripts are listed. But only a sample of the Byzantine texts are listed as the greater number of these precludes listing them all.   And finally, most modern-day versions are based on the CT. Among these are the New American Standard Bible, the New International Version and the New Revised Standard Version (the above information gleaned from many sources). 

As previously mentioned, 15% of the NT text differs between the manuscripts. But of these variants more often than not, it is vary easy to determine which reading is a "mistake" and which is correct. As such, the above mentioned, published Greet texts are very similar in their handling of the variants. The TR agrees with the MT 99% of the time in its handling of variants and the CT agrees with the MT 98% of the time. So there is only a 1-2% difference overall between these published Greek texts.  Moreover, the majority of variants among manuscripts and between the above mentioned, Greek texts are insignificant, some variations exist in the spelling of Greek words, in word order, and in similar details. These ordinarily do not show up in translation and do not affect the sense of the text in any way. 

Following are examples of these types of variants which can be seen by comparing a version based on the MT (or TR) with one based on the CT. The MT reading will be given first and the CT reading afterwards. 

First, in Matthew 13:55 the name of one of Jesus' half-brothers is "Joses" in the MT, but "Joseph" in the CT. The difference is only one letter in the Greek. The MT name ends with a sigma while the CT has a phi. The sounds are somewhat similar.  Moreover, since Jesus' step-father was named Joseph, it is easy to see how a scribe could assume one of Jesus' step-brothers would also be named Joseph and misread the word. And slight differences in the spelling of proper nouns account for a large portion of the variants found between NT manuscripts.  Second, a simple case of word order change can be seen in Luke 17:23. In the MT, the false prophets shout, "Look here! or Look there!" But in the CT the shout is, "Look there! or Look here!" Not exactly an earthshaking difference.  And finally, in Acts 1:8, Jesus either commands Christians to be witness "to Me" or "of Me." Again, in Greek, the difference is one letter. Moreover, the Greek words involved are homonyms (moi vs. mou). 

Since the early scribes often read the text as they were copying from it, or the text was dictated to a room full of scribes, the reason for this variant is obvious. Moreover, this writer has often typed the wrong word when there is another which sounds exactly like it. Particularly troublesome has been "there" vs. "their." 

Furthermore, most of the textual variants are similar to the above examples. And anyone who has ever done much typing or hand copying can easily understand how such simple mistakes can be made. But when someone else reads the text, the mistake is generally noticed. It the same with the Greek variants. In most cases, which variant is correct is obvious, and both the MT and the CT have the same reading. 

Moreover, "Fortunately, if the great number of manuscripts increases the number of errors, it increases proportionally the means of correcting such errors, so that the margin of doubt left in the process or recovering the exact original wording is not so large as might be feared; it is in truth remarkably small" (Bruce, 19). 

Thus, when there are differences between manuscripts, more often than not, the correct reading is easily determined. And even when it is not, the variant is generally insignificant.  However, there are some important variants. And for these, the evidence is often divided as to which is the original reading. And, often, the MT follows one reading and the CT another. And it is because of these that there is the heated debates among scholars as to whether the MT or the CT best reflects the original. But, in cases like this, most modern-day versions will footnote the variant. The footnotes in the NKJV are particular helpful in this regard. In this version, any significant variants between the TR which it based on, the MT and the CT are specifically indicated in its textual footnotes. 

The reasons for the differences between the Majority Text and the Critical Text are much more complicated than the simple points mentioned above. And trying to decide whether the MT or CT best reflects the autographs is even more complex, although very interesting.  Here, it will just be emphasized that- 
 
Bible readers may be assured that the most important differences in English New Testaments of today are due, not to manuscript divergence, but to the way in which translators view the task of translation. How literally should the text be rendered? How does the translator view the matter of biblical inspiration?

________, ed. Synopsis Quattuor Evangeliorum: Locis Parallelis Evangeliorum Apocryphorum et Patrum Adhibitis. 13th rev. ed. Stuttgart: Deutsche Bibelgeselleschaft, 1985. 
Has editorial material in German, Latin, and English. The text of this harmony is in Greek and covers the patristic writings, thus making it more comprehensive than the Greek-English edition. Available through the American Bible Society. 
BS2560 .A2 1985 

________. Synopsis of the Four Gospels: Greek-English Edition of the Synopsis Quattuor Evangelorium. 7th ed. Stuttgart: German Bible Society, 1984. 
This harmony has the convenience of the Greek text of the Nestle-Aland 26th ed. with RSV translation facing. Its disadvantage is, of course, the absence of the patristic writings. 
BS60 .A2 1984 

Colwell, Ernest C. Studies in Methodology in Textual Criticism of the New Testament. New Testament Text and Tools, vol. 9. Grand Rapids: Wm. B. Eerdmans Pub. Co., 1969. 
Collection of 11 essays dealing with methods in grouping NT MSS, locating a newly discovered MS, establishing the nature of text types, and dating MSS. Very important tool which carefully details the methods of approach. 
BS2325.C727s 

Elliott, James K. A Survey of Manuscripts Used in Editions of the Greek New Testament.Supplements to NovTest, Vol. 57. Leiden; New York: E. J. Brill, 1987. 
The major portion of the book is a series of tables showing how all the available MSS are used in 8 Greek NT's, 3 synopses, and the IGNTP on Luke. It should help those who have interest in studying certain MSS and wish to assemble an apparatus. 
BS1939 .E57 1987 

Epp, Eldon J., and Fee, Gordon D. eds. New Testament Textual Criticism: Its Significance for Exegesis. Oxford: Clarendon Press; New York: Oxford University Press, 1981. 
This Festschrift to Bruce Metzger, brings together the expertise of several international scholars in the field of textual criticism; the essays deal with selected NT problem texts. 
BS2325 .N49 

________. Studies in the Theory and Method of New Testament Textual Criticism. Grand Rapids: Eerdmans, 1993. 
The seventeen studies in this volume provide  in-depth presentations and assessments of past and current methods applied to the New Testament text. The volume offers a general and historical overview of the discipline, definitions of key terms, critiques of current theory and method, methods of establishing textual relationships, studies of the papyri with respect to text-critical method, and guidelines for the use of patristic evidence. 
BS2325 .E66 1993 
 

________. "The Eclectic Method in New Testament Textual Criticism: Solution or Symptom?" HTR 69 (July-October 1976): 211-57. 
Very important article which shows how the eclectic method in NT textual criticism, while claiming to provide a solution to the impasse between the different criteria for determining originality, nevertheless, obscures the problems of the discipline. 
BR1 .H35 v. 69 

________. "New Testament Textual Criticism in America: Requiem for a Discipline." JBL 98 (March 1979): 94-98. 
After a brief survey of the work done by North American text critics Epp gives reasons for the decline of the discipline on this continent. 
BS410 .J6 v. 98 

________. "An Indispensable but Flawed Tool for Textual Critics." Int 44 (January 1990): 71-75. 
This review essay of Kurt and Barbara Aland's Text of the NT (1st ed.) is a stinging rebuke of the authors' neglect to treat and/or mention textual traditions and methods of classification (e.g., The Profile Method) other than the one they adopt. 
BR1. I54 v. 44 

Finegan, Jack. Encountering New Testament Manuscripts: A Working Introduction to Textual Criticism. Grand Rapids: Eerdmans Pub. Co., 1974. 
Not only does this work give a clear account of what is involved in the discipline of textual criticism, but it simulates for the student the actual experience of seeing and reading the MSS. 
BS2325 .F56 1974 

Greenlee, J. Harold. Introduction to New Testament Textual Criticism. Grand Rapids: Eerdmans, 1964. 
A good manual for beginners; author gives helpful hints on how to read the critical apparatus of various Greek New Testament. 
BS2325 .G67 

Kilpatrick, George D. The Principles and Practice of New Testament Textual Criticism. Leuven: Leuven University Press, 1990. 
The author emphasizes that a painstaking consideration needs to be given to the principles of textual criticism, to the significance of the Western text, and to the distribution of vocabulary items and variation of grammatical usage in various writers. 
BS2393 .K555 1990 

Metzger, Bruce M. The Text of the New Testament: Its Transmission, Corruption, and Restoration. 2nd ed. Oxford: Clarendon Press, 1968. 
Still very up-to-date, and perhaps the most comprehensive manual on the subject by the leading NT text critic in North America.  A must for every Ph.D student. 
BS2385 .M41t2 

________. A Textual Commentary on the New Testament: A Companion Volume to the United Bible Societies Greek New Testament. (3rd ed.) London; New York: United Bible Societies, 1975. 
Explains the rationale underlying the committee's choice of most of the difficult textual variants for the UBS Greek New Testament, 3rd ed. Also has helpful bibliogra-phical references. 
BS2325 .M43 1975 

Nestle, Eberhard. Introduction to the Textual Criticism of the Greek New Testament. Trans. by William Edie. New York: G. P. Putnam's Sons, 1901. 
Gives brief history of the printed text, then discusses the artifacts of textual criticism, and finally shows how the science of textual criticism works. The student should not ignore a textbook of this nature by one who has given the NT text a certain tradition. 
BS1938 .N43 

Parvis, Merrill M., and Wikgren, Allan P. eds. New Testament Manuscript Studies: The Materials and the Making of a Critical Apparatus. Chicago: University of Chicago Press, 1950. 
This collection of essays by leading NT scholars in the field of textual criticism intended to indicate the state of the discipline at that time, and also to propose methods of arriving at a new apparatus for the Greek New Testament which was to be published shortly. 
BS1938 .P3 

Richards, W. L. "A Critique of a New Testament Text-Critical Methodology--the Claremont Profile Method." JBL 96 (December 1977): 555-66. 
The article evaluates the Claremont Profile Method (CPM), articulated by Wisse et al.; by applying the method to 1 John the author shows the weakness of the CPM. 
BS410 .J6 v. 96 

Robertson, A. T. An Introduction to the Textual Criticism of the New Testament. New York: George H. Doran Co., 1925. 
A dated text but still helpful if one wants to understand the perspective from which some earlier practitioners proceeded. Follows the approach taken by B. B. Warfield to whom the book is dedicated. 
BS2385 .R799i 

Taylor, Vincent. The Text of the New Testament: A Short Introduction. New York: St.Martin's Press, 1961. 
Provides a preliminary base to enter the discussions of such earlier masters as Westcott, Hort, F.G. Kenyon, Souter, Lake, and Streeter. The very helpful notes on the selected readings should not be neglected. 
BS2350 .T24t 

Vaganay, Leon. An Introduction to the Textual Criticism of the New Testament. Trans. by B. V. Miller. London and Glasgow: Sands & Co., 1937. 
Very useful handbook which gives extended entries for most of the jargon for NT text criticism. Chapter on method is dealt with in a less complicated manner than most of the other texts. 
BS2385 .V12, Revised Edition BS2385 .V3212 1991 

Vincent, Marvin R. A History of the Textual Criticism of the New Testament. London: Macmillan & Co., 1889. 
Useful for an understanding of the historical development of the discipline up to the end of the 19th century, concluding with the work of Bernhard Weiss. 
BS2385 .V5 

Wisse, Frederik. The Profile Method for the Classification and Evaluation of ManuscriptEvidence, as Applied to the Continuous Greek Text of the Gospel of Luke. Grand Rapids: Wm. B. Eerdmans, 1982. 
The outgrowth of a Claremont dissertation directed by E.C. Colwell. The method is associated with the International Greek New Testament Project (IGNTP) at Claremont, and first proposed by Eldon Epp as a method for classifying and evaluating Byzantine NT MSS. 
BS1939 .W57 1982