# Worker > See first: [User docs | Worker](#worker-cont) In Juju, a **worker** is any type that implements [the worker interface](https://documentation.ubuntu.com/juju/4.0/contributor/reference/worker-interface.md#worker-interface). Examples of workers include [the dependency engine](https://documentation.ubuntu.com/juju/4.0/contributor/reference/dependency-package.md#newengine), instances run by the dependency engine (the typical usage of the term “worker”), and [watchers](https://github.com/juju/juju/blob/HEAD/core/watcher/watcher.go). A Juju [agent](https://documentation.ubuntu.com/juju/4.0/contributor/reference/agent.md#agent-cont) runs one or more workers at the same time in parallel. A worker may run / be run by another worker.