Electroweak interactions need three Nambu--Goldstone bosons to provide a mass to the W and the Z gauge bosons but they also need an ultra-violet moderator or new physics to unitarize the gauge boson scattering amplitudes. Electroweak precision data seem to favour the existence of a light scalar degree of freedom but this 'Higgs boson' does not have to be a fundamental particle. I shall elaborate on the idea that it could be a dynamical composite bound state emerging from a strongly interacting sector, and I shall argue that such composite Higgs scenarios offer a continuous deformation away from the Standard Model controlled by a few parameters only. I shall discuss phenomenological signatures of such models both at the LHC and at a Linear Collider.
