Electron paramagnetic resonance (EPR) has been used to identify and characterize point defects in lithium triborate (LiB3O5) crystals grown for nonlinear optical applications. As-grown crystals contain oxygen vacancies and lithium vacancies (as well as trace amounts of transition-metal ions in a few samples). Exposing a crystal to ionizing radiation at 77 K produces “free” electrons and holes. These electrons are trapped at the pre-existing oxygen vacancies and give rise to an EPR signal with a large hyperfine from one 11B nucleus. The corresponding holes become self-trapped on oxygen ions as a result of the significant lattice relaxation of a nearest-neighbor fourfold-bonded boron ion. This gives rise to an EPR signal with a smaller 11B hyperfine pattern due to the oxygen’s threefold bonded boron neighbor. Warming the crystal to approximately 130 K destroys the self-trapped hole centers that were initially formed, and allows a second holelike signal to be observed (which in turn decays between 150 and 200 K). The structure of the second hole center is very similar to the self-trapped hole center and a neighboring lithium vacancy makes this latter center more thermally stable. The EPR spectra from Ni+ and Cu2+ ions are also reported.