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Thedevelopmentofa high-data-rate communications electronics subsystem for future application ul free-space, directdetection laser communications is described. The dualchannel subsystem uses quaternary pulse position modulation (QPPM)* and operates at a throughput of 650 megabits per second. Transmitting functions described include source data multiplexing, channel data demultiplexing, and QPPM symbol encoding. Receiving functions include analog signal conditioning, slot and symbol clock recovery, QPPM data recovery and decoding, channel data multiplexing, and destination data dernultiplexhig. Implementation of a prototype version in discrete gallium arsenide logic, radiofrequency components, and microstrip circuitry is presented. The approach to developing an integrated package for potential spaceflight demonstration is described. Link effects simulation, full-duplex data and video communications demonstration, and computer control and monitoring approaches are discussed. Packaging of the communications electronics subsystem and plans for future development conclude the paper.