I've pretty much always used send() with sockets and now I'm moving onto the WSA functions. With send(), I have a sendall() helper that ensured all data is delivered even if it didn't happen in one try and a partial send occurred on first call. So, instead of learning the hard way or over-complicating code when I don't have to, decided to ask you: Can a blocking WSASend() send partial data or does it send everything before it returns or fails? Or should I check the bytes sent vs. expected to send and keep at it until everything is delivered? ANSWER: Overlapped WSASend() does not send partial data but if it does, it means the connection has terminated. I've never encountered the case yet.