In this paper we present key elements of a peer to peer (P2P) based software architecture for integrated and collaborative product engineering. We argue that distributed and cross-enterprise product lifecycle management can benefit from the availability of decentrally managed product model repositories. We present the overall system architecture of a platform called Peer-to-Peer Product Collaboration Platform (PCP). Our work, while driven from business level issues such as supporting the emergence of organizations, partnerships, and processes for collaborative and cross-enterprise PLM, focuses on aspects of ICT level interoperability. It aims at enabling loosely coupled interaction between changing partners in a decentral environment, where traditional hierarchical client-server based architecture may not be applicable.