**Docker** is an open-source [[Platform as a service|platform-as-a-service]] product that uses [[OS-level virtualization|operating system-level virtualization]] to deliver [[Software|software]] in packages called [[Container (virtualization)|containers]]. Containers bundle an application's code together with its dependencies, libraries, and configuration files, allowing the software to run consistently across different computing environments. Developed by [[Solomon Hykes]] and first released in 2013 by Docker, Inc. (formerly dotCloud), Docker became one of the most widely adopted tools in modern [[Software development|software development]] and [[DevOps|DevOps]] practice. Docker builds on [[Linux kernel|Linux kernel]] features including [[cgroups|control groups]] (cgroups) and [[Linux namespaces|namespaces]] to provide process isolation without the overhead of full [[Virtual machine|virtual machines]]. The core components of the Docker platform include the Docker Engine, a client–server application that creates and manages containers; the [[Docker Hub|Docker Hub]] registry, a cloud-based repository for sharing container images; and Docker Compose, a tool for defining and running multi-container applications. Container images are constructed from layered filesystems using a declarative configuration file called a Dockerfile, enabling reproducible and version-controlled build processes. Docker played a central role in popularizing container-based [[Software deployment|software deployment]] and directly influenced the development of broader container ecosystem tooling. Its widespread adoption prompted the establishment of the [[Open Container Initiative]] (OCI) in 2015 under the [[Linux Foundation]], which standardized container image and runtime specifications to promote interoperability. Docker's architecture also laid conceptual groundwork for [[Container orchestration|container orchestration]] platforms such as [[Kubernetes]], which automates the deployment, scaling, and management of containerized applications at scale. While Kubernetes and other platforms have in some contexts supplanted Docker as the default runtime in production environments, Docker remains the dominant tool for local development and image authoring workflows.