  We introduce the Vainshtein mechanism which plays a crucial role in massive
gravities, as well as in related theories such as Galileons and their
extensions. This mechanism, also known as k-mouflage, allows to hide via non
linear effects - typically for source distances smaller than a so-called
Vainshtein radius which depends on the source and on the theory considered -
some degrees of freedom whose effects are then only left important at large
distances, e.g. for cosmology. It is introduced here in non linear Fierz-Pauli
theories (massive gravities), including the dRGT theories, in their decoupling
limits, as well as in other models such as DGP model or generalized Galileons.
This presentation is self-contained and before discussing the Vainshtein
mechanism we introduce some useful results and concepts concerning massive
gravity, such as the vDVZ discontinuity, the decoupling limits or the
Boulware-Deser ghost.
