The Electron Losses and Fields Investigation (ELFIN) is a 3U+ CubeSat mission under development by the Earth, Planetary, and Space Sciences department at UCLA. ELFIN will explore the mechanisms responsible for the loss of relativistic electrons from the radiation belts. ELFIN is funded jointly by the NSF CubeSat and NASA LCAS programs and has been a participant in the AFRL’s University Nanosatellite Program.