Much has been learned in the last decade about concurrent programming.. This patmr identifies the major concepts of concurrent programming and describes some of the more importam language notations for writing concurrent programs. The roles of processes, communication, and synchronization are discussed. Language notations for expressing concurrent execution and for specifying process interaction are surveyed. Synchronization primitives based on shared variables and on message passing are described. Finally, three general classes of concurrent programming languages are identified and compared.