Queuing is a programming technique in which two programs exchange data asynchronously, without calling one another directly. Using queuing, two programs communicate by passing messages to one another via a queue. Conceptually, a queue is like an "inbox." When one program wants another program to process a piece of information, it simply puts that information into the other program's queue. On the other end, the receiving program monitors its designated queue and processes messages that other programs deposit in it.

Systems that interface with one another through queuing never interact directly; they only interact with their queues. In fact, a program might not process its queue until hours, days, or weeks after another program deposits a message in it.