Astrophysics and particle physics with cosmic-ray electrons and positrons

Cosmic rays are predominantly nuclei, in particular protons.  However, the less abundant cosmic-ray electrons and positrons are also important probes of open questions in astrophysics and particle physics.  The Fermi Gamma Ray Space Telescope, designed to study the high-energy universe with gamma rays, is also an excellent electron and positron detector.  Ground-based imaging atmospheric Cherenkov telescopes have also measured cosmic-ray electrons and positrons up to several TeV.  PAMELA, Fermi, and AMS have discovered a surprising excess of positrons between 10 GeV and 350 GeV.  I will describe these measurements and their implications for astrophysics and particle physics, as well as prospects for future measurements.