Rmecent developments in the field of chemical microsensors are leading to new applications for which these devices have the potential to supplement or replace traditional analytical chemical instrumentation. The fundamentals of current microelectronic, acoustic wave, optical fiber, and electrochemical microsensors are presented, and a few recent, exciting results in these areas are described. Although future opportunities in the microsensor field are numerous, many significant problems, the majority of them related to the materials utilized for the chemically sensitive layers that are the "front end" of these devices, remain to be explored and solved.