When a cell migrates, it generates traction forces on the underlying substrate. The cell traction force (CTF) is not only essential for cell migration, but it is also used by cells to control their shape and maintain cellular homeostasis. As such, quantification of CTFs aids in better understanding of many fundamental biological processes such as morphogenesis, angiogenesis, and wound healing of tissues and organs. A new technology called cell traction force microscopy (CTFM) has been developed to determine CTFs in a quantitative fashion. The advantage of this technology is that it directly measures the "cause" (i.e., CTFs) of cell movement instead of the "effect" (i.e., cell movement itself), which is measured by various conventional methods. This chapter provides detailed information of materials and methods that are needed in order to perform typical CTFM experiments. Several examples are also given to illustrate various applications of CTFM in cell biology research.