Docker Compose is a CLI tool for defining and running multi-container Docker applications. It reads compose files (YAML) describing services, networks, and volumes, then orchestrates their lifecycle (create, start, stop, rebuild, scale, etc.) against the Docker Engine API. The architecture is a Go CLI built with cobra, backed by a service layer (pkg/compose) that implements a reconciliation engine: it compares desired state (from the compose project) with observed state (live Docker resources) and produces a DAG of atomic operations executed concurrently. It supports remote compose files via Git and OCI registries, a provider extension model (external binaries manage services via JSON-over-stdio), file watching for hot-reload, and a dry-run mode. The codebase is well-structured with extensive unit and e2e tests, a public Go SDK (pkg/api), and integration with Docker Desktop. Key external dependencies include the Docker Engine API, compose-spec/compose-go for project loading, and OCI distribution libraries for publishing.