Middleware is the third component in a two-system integration, and it exists because some business rules do not belong cleanly to either side. The ERP knows the contract price but not the browsing session. The storefront knows the session but not the price rule. Something has to hold the logic that turns one into the other.
It comes in two shapes. A hosted integration platform gives you connectors, retries, logging and a place to see failures, in exchange for a subscription and someone else deciding when things change. A custom service gives you exactly the behaviour you specified, in exchange for owning it: the deployment, the monitoring, the on-call, and the work every time the ERP has a release.
The reason to reach for it is not sophistication. It is that a native connector has stopped being able to express what your business does, and the alternative is a growing pile of workarounds spread across two systems that nobody is maintaining. Middleware makes that logic one thing, in one place, that you can test.
Why it decides a platform
Middleware is what you reach for when the business logic does not live cleanly in either system. It adds a component to own and maintain, and it is often the only honest answer for a complex B2B seller.
Also called: integration layer, iPaaS.
Last updated 2026-08-20.