Software product lines aim in having a common platform from which several similar products can be derived. The elements of the platform are called assets and they are managed in an asset base being part of the product line infrastructure. Assets can include own developments, open source or third-party software modules, as well as design and project documents. In the context of the European-wide project FAMILIES we concentrated on techniques used to populate the asset base by recovering assets from existing systems. We present an approach on how to incorporate existing assets into the product line infrastructure. Thereby we explicitly distinguish the asset origins and the different information sources available. The incorporation is a quality-driven process that is backed up by a set of reverse engineering techniques to evaluate the asset?s internal quality. The quality assessment of an asset is the critical measurement for industrial development organizations in order to incorporate assets into their product line infrastructure.