The algorithms and methods of Peer-to-Peer (P2P) technology are often applied to networks and services with a high demand for scalability. The huge number of peers, the state space, as well as the interactions and relationships between peers and states often makes an analytical description intractable. Discrete event simulation is a tool which is able to incorporate all interactions and parameters and may reflect reality as accurately as possible. Large scale simulations, however, also require sufficient memory capacities and often exceed the available computational power: it might already be a problem just to keep the states of the peers in the main memory. The 7th International Workshop on Modeling, Simulation, and Optimization of Peer-to-peer environments (MSOP2P) aims at bringing together researchers and practitioners from academia, industry and government to advance the state of the art in modeling, simulating and optimizing P2P environments. The workshop also offers the opportunity to discuss different techniques to make P2P simulations scalable, to debate the advantages and disadvantages of a simulation on packet level or on application level, and to compare analytical models as well as emulations to results gained by simulation. The general venue will be a good occasion to share, to learn, and to discuss the latest results in this field of research.