What is Continuous Integration (CI)?

Continuous Integration (CI) is the practice of automatically building and testing code every time a developer pushes changes to a shared repository, typically multiple times per day. The goal is to detect integration bugs as early as possible — when they are cheapest to fix — rather than discovering them weeks later when many changes have accumulated. A CI server (GitHub Actions, Jenkins, GitLab CI) monitors the repository, triggers a pipeline on each push, compiles the code, runs the test suite, and reports the result back to the developer. CI enforces a culture where the main branch is always in a buildable, tested state. Martin Fowler, who popularized the term, emphasizes that the practice is as much about culture (frequent small commits, fixing broken builds immediately) as it is about tooling.