A number of particle accelerators worldwide require RF crab cavities for a number of applications, including maximizing collision luminosity, production of short X- ray pulses, and diagnostics. The Cockcroft Institute has led the development crab cavities for the LHC, ELC and CLIC colliders. The design for each of these cavities is very different due to the different bunch structures in each accelerator. For the CLIC accelerator we have chosen an X-band traveling wave normal conducting cavity, the ILC uses an S-band superconducting cavity and the LHC is proposed to use a novel compact shape superconducting cavity with an operating frequency between 200-800 MHz. The general design considerations for crab cavities will be discussed as well as special constraints for each of the three systems and their current designs.