I will present a new paradigm for achieving thermal relic dark matter. The freezeout process is a number-changing 3-to-2 annihilation of strongly-interacting-massive-particles (SIMPs) in the dark sector, and points to sub-GeV dark matter. The couplings to the visible sector, necessary for maintaining thermal equilibrium with the Standard Model, imply measurable signals that will allow coverage of a significant part of the parameter space with future indirect- and direct-detection experiments and direct production at colliders. Moreover, 3-to-2 annihilations typically predict sizable 2-to-2 self-interactions which naturally address small scale structure puzzles. I will show how the mechanism is realized in simple classes of QCD-like theories, where the pions play the role of dark matter.