The IGDA Online Games SIG Persistent Worlds White Paper is intended to provide a summary of contemporary issues in the development and operation of massively multi-player online persistent worlds. We have chosen to use the title Persistent State World or PSW to describe these online experiences. Also used are the terms: virtual world, multi-user domain or multi-user dungeon (MUD), massively multi-player (MMP) game, massively multiplayer online game (MMOG) and massively multi-player online role-playing game (MMORPG). The sheer variety of acronyms and the inadequacy of all of them are indicative of the youth of this industry. In particular the authors point out that the growth of the persistent worlds market is almost predicated upon its moving away from its origins in fantasy role-playing type games. Our intention is to provide a broad survey of the market, primarily in the US with some examples from overseas, an overview of design and production, a guide to technology practices and an introduction to the rigors of service and operations. The focus of this paper is to provide developers, operators and publishers of persistent worlds with information to help them decide whether or not to proceed with development; to identify pitfalls along the way; to deliver; and then to support these games successfully. The field of PSW development and operation is enormously complex and we cannot hope to be exhaustive or complete in our overview, but we hope that developers new to the field, as well as old hands, will find some useful information within.