The 4th IGPP Astrophysics Conference proceedings discuss various aspects of collisionless shock physics in solar system plasmas, including: the microstructure of collisionless shocks, wave activities at and near shocks, particle acceleration at collisionless shocks and collisionless shocks in the outer heliosphere. This volume can serve both as a summary of the current understanding of collisionless shock physics and as a starting point for future research, especially for young scientists in this field.