Every project has to deal with dependencies and CMake makes it relatively easy to find out whether these dependencies are present on the system where we configure our project. Chapter 3, Detecting External Libraries and Programs, showed how to find dependencies installed on the system and we have used that same pattern so far. However, if dependencies are not satisfied, the most we can achieve is fail the configuration and alert the user of the reasons for such a failure. However, with CMake it is possible to organize our projects such that dependencies can be automatically fetched and built if they are not found on the system. This chapter will present and analyze the ExternalProject.cmake and FetchContent.cmake standard modules and their use in the superbuild pattern. The former allows us to retrieve the dependencies of our project at build time and has been a part of CMake for a long time. The latter module was added in version 3.11 of CMake and allows us to retrieve dependencies at configure time. With the superbuild pattern, we can effectively leverage CMake as an advanced package manager: within your project you will handle dependencies in the same manner, whether already available on the system or whether they need to be built from scratch. The next five recipes will walk you through the pattern and show how it can be used to fetch and build virtually any dependency.