In unreliable connectionless communication, single messages are transmitted between sender and receiver. A message may or may not arrive correctly at its destination. While such communication has low overhead, it requires that the application manage errors. This chapter expands the UICI library to include facilities for connectionless communication with timeouts and error checking. The chapter develops applications of the simple-request and request-reply protocols based on the connectionless interface. The UICI connectionless interface is then implemented with sockets, using UDP. UICI UDP also includes functions for multicast communication.