This chapter reviews recent developments in the application of single-molecule spectroscopy (SMS) to studies of enzyme kinetics and mechanism. Protocols for conducting single-molecule experiments on enzymes, based largely on the experience in our laboratory, are provided, including methods of sample preparation, instrumentation, and data analysis. We also address general issues related to the design of meaningful single-molecule experiments and include specific examples of the application of SMS to enzyme studies, which reveal new and intriguing aspects of enzyme behavior, including static and dynamic heterogeneity, as well as subunit cooperativity. Finally, we discuss the advantages of employing single-molecule approach in obtaining new information beyond ensemble studies.