Shock waves in interstellar medium are collisionless and the shock transition is by the collective motion of underlying plasma (e.g., MHD turbulence). Two important consequences of collisionlesss shocks are 1) they do not partition energy equally among di?erent particle species, and 2) they accelerate cosmic rays. Balmer-dominated filaments, which represent fast non-radiative shocks into partially neutral medium, provide unique diagnostics for collisionless shocks. I'll review recent observations of Balmer-dominated filaments and their implication on the physics of collisionless shocks. In particular, I'll discuss how observations of Balmer-dominated filaments can constrain the cosmic ray acceleration process.