This document summarizes asynchronous input/output in WinSock. It discusses how the message-driven architecture of Windows can cause problems for blocking socket calls. It then describes three methods for asynchronous notification in WinSock - message-driven using WSAAsyncSelect(), event-driven using WSAEventSelect(), and callback routines. It provides examples of using WSAAsyncSelect() and WSAEventSelect() to select event types and receive asynchronous notifications for sockets.