The Swarm Development Group (SDG) was founded in September 1999 as a private, not-for-profit [501c(3)] organization to support the development of the Swarm Simulation System (Swarm) and the interests of the group members. The purposes of the SDG are to: 1. advance the state-of-the-art in multi agent based simulation through the continued advancement of the Swarm Simulation System and support of the Swarm user community 2. promote the free interchange of multi agent based simulations among computing specialists and the public 3. develop and maintain the integrity and competence of individuals engaged in the practice of agent based simulation. Agent-based models (ABMs) are an exciting new approach for learning about and simulating complex systems, and its use is growing rapidly in science and business. As opposed to traditional modeling techniques that represent systems via differential equations for system state, ABMs represent systems as a collection of digital individuals that each have unique characteristics, interact with each other and their environment, and exhibit adaptive behavior. Swarm is a platform for ABMs that includes: a conceptual framework for designing, describing, and conducting experiments on ABMs; software implementing that framework and providing many handy tools; and a community of users and developers that share ideas, software, and experience. Swarm was the first of several agent-based modeling platforms that are widely used by scientists and students studying complexity in many fields of science. Swarm was originally developed in the mid-1990s by Chris Langton at the Santa Fe Institute and has an active, international user community. Swarm software is a library of Objective-C classes; users code their models in Objective-C, Java, or C++.