High power input couplers are a fundamental component of linear accelerating structures and, in particular, of superconducting structures. In fact, in this case, the power coupler's function is not only power transfer and vacuum separation but also includes the thermal transition and the integrity of the cavity cleanliness. A lot of activity has been recently carried out in the framework of different project on both CW (KEK and Cornell) and pulsed (SNS and TTF) power couplers. Special attention has been devoted during the design phase to take care of the thermo-mechanical and electromagnetic performances, the multipacting thresholds, the preparation procedures and, last but not least, the cost which in the case of high energy linacs is a critical issue. In this framework not only the design phase but also the conditioning of the couplers has stimulated different studies. Partial reviews of the existing designs and of the couplers characteristics will be presented taking into account the different challenges.