In web applications that use OWIN the application developer must configure an OWIN pipeline. Requests received by the web server are pushed through the pipeline until a middleware chooses to handle the request. Upstream middleware refers to middleware that is positioned further up the pipeline than the current one, and has already been given an opportunity to handle the request before the currently executing one.

There is an upstream communication mechanism in the OWIN Framework that allows a middleware to pass information to middleware that is upstream, i.e. nearer the front of the pipeline.