Bottom-Up Technologies for Reuse (BUT4Reuse) is a generic and extensible framework for helping in Software Product Line (SPL) adoption from existing artefacts. It supports the re-engineering of source code variants, models, requirements, or other structured formats. Currently 17 adapters are available for different artefact types. The framework covers the most relevant re-engineering activities towards extractive SPL adoption, i.e., the same framework can support feature identification and location, feature constraints discovery, feature model synthesis, and the construction of reusable assets. Well-defined extension points are provided for integrating algorithms and techniques for the mentioned activities. Similar to the case of the adapters, more than 20 state-of-the-art algorithms and techniques are currently integrated. The target users are both SPL adopters and integrators of adapters and techniques. In addition, two integrated benchmarks are proposed towards reproducible and comparable results for feature location research. This chapter presents the framework principles, supported activities, and an overview of the currently available functionalities.