A model is presented for the energization and thermalization of the ions traversing the earth's bow shock under quasi-perpendicular conditions. This model is able to account for amny of the features of particle and field measurements at and behind the shock and does not involve an unobserved subshock or strong ion heating instability. Rather the ions are energized and begin to thermalize by gyration and counterstreaming effects in the macroscopic fields of the shock. Experiments to test this model may be carried out in the course of the International Magnetospheric Study.