Although solar activity may significantly impact the global environment as well as socio-economic systems, the mechanisms for solar eruptions and the subsequent processes have not yet been fully understood. Thus, modern society, which is supported by advanced information systems, is at a risk from severe space weather disturbances. Project for Solar-Terrestrial Environment Prediction (PSTEP) was launched in order to improve this situation through synergy between the basic science research and the forecast operation. PSTEP is a nation-wide research collaboration supported by a Grant-in-Aid for Scientific Research on Innovative Areas from MEXT/Japan. By this project, we seek to answer some of the fundamental questions concerning the solar-terrestrial environmental system, and aim to contribute to building a next-generation space weather forecast system to prepare for severe space weather disasters. PSTEP is organized by four research groups (A01–A04) and proposal-based research units.