Since their introduction to biomagnetism in 1970, SQUID magnetometers have been used worldwide to measure magnetic signals from the heart, brain, lungs, liver, nerves, skeletal muscle, stomach, intestines, eyes, and other organs. The majority of the effort in the field has been by university and national-laboratory researchers and by small, high-technology companies, and has been directed towards the development and promotion of this technology. While a SQUID clearly is an accepted and productive research instrument, the application of this technology in routine clinical diagnosis is only now beginning. The challenge is to identify applications for which SQUIDs are ideally suited and there is minimal competition from other technologies. The introduction of high-temperature superconductor (HTS) SQUIDs has led to a resurgence, for example, in measurements of the magnetocardiogram by physicists and new searches for applications. Similar trends are evident in the use of SQUIDs for the nondestructive evaluation (NDE) of aircraft and other structural systems and materials: most of the effort is directed towards instrumentation development and demonstrations in simple systems. Instruments suitable for specific commercial applications are just now being prototyped, and there is a new generation of HTS SQUIDs for NDE. This chapter presents an overview of SQUID magnetometers for biomagnetism and NDE, reviews a number of pertinent applications of SQUIDs, and discusses the criteria for successful application. © 2000 Kluwer Academic Publishers.