POET (Polarimeters for Energetic Transients) represents a concept for a NASA Small Explorer (SMEX) satellite mission, whose principal scientific goal is to understand the structure of GRB sources through sensitive X-ray and γ-ray polarization measurements. The payload consists of two wide field-of-view (FoV) instruments: a low-energy polarimeter (LEP) capable of polarization measurements in the energy range from 2–15 keV and a high-energy polarimeter (Gamma-Ray Polarimeter Experiment or GRAPE) that would measure polarization in the 60–500 keV energy range. The POET spacecraft provides a rotating zenith-pointed platform for dealing with any residual systematic effects in the polarization response and for maximizing the exposure to deep space. POET would be capable of measuring statistically significant polarization (for polarization levels in excess of 20%) for ∼80 GRBs in a two-year mission. High-energy polarization data would also be obtained for SGRs, solar flares, pulsars and other sources of astronomical interest.