Monorepos, which store an entire codebase in a single repository, offer centralized control over modules and dependencies, making them a popular choice among large companies like Google, Dropbox, LinkedIn, and Uber. The open-source build tool Bazel, developed by Google, enhances the efficiency of monorepos by supporting multiple languages and platforms, enabling fast builds through caching, and allowing for complex operations on binaries and scripts using its Python-like language, Starlark. While Bazel provides greater structure and language support for large projects, it also presents challenges such as a steep learning curve due to its divergence from established dependency management patterns, and potential security risks in exposing entire codebases in large teams. Despite these challenges, Bazel's robust configurational files and documentation make it a viable option for large multi-language projects, and alternatives like Earthly offer additional support for monorepo and polyrepo setups with a more gradual learning curve.