An overview of optical data communications is provided, beginning with a brief history and discussion of the unique requirements that distinguish this subfield from related areas such as telecommunications. Each of the major datacom standards is then discussed, including the physical layer specification, distances and data rates, fiber and connector types, data frame structures, and network considerations. These standards can be categorized by their prevailing applications, either storage [Enterprise System Connection (ESCON), Fiber Channel Connection (FICON), and Fibre Channel], coupling (Fibre Channel), or networking [Fiber Distributed Data Interface (FDDI), Gigabit Ethernet, and asynchronous transfer mode/synchronous optical network (ATM/ SONET)]. We also present some emerging technologies and their applications, including parallel optical interconnects, plastic optical fiber, wavelength multiplexing, and free-space optical links. We conclude with some cost/performance trade-offs and predictions of future bandwidth trends.