Code review, a practice that significantly enhances code quality and prevents bugs, has evolved remarkably since its inception. Originating in the 1970s with IBM engineer Michael Fagan's concept of "Fagan Inspections," it initially involved meticulous, in-person code examinations. The 1990s introduced desk checks, where developers self-reviewed their work before others assessed it. The digital transition in the early 2000s marked a pivotal shift, with tools like Google's Mondrian and later GitHub revolutionizing the process by allowing global collaboration through web-based reviews. Mondrian, inspired by Gmail, focused on individual code changes, while GitHub emphasized open-source collaboration through repositories and pull requests. Today, code review systems are tailored for both open-source and closed-source environments, supporting diverse collaboration needs and marking a significant progression from their paper-based origins.