  Fundamental questions on the nature of matter and energy have found answers
thanks to the use of particle accelerators. Societal applications, such as
cancer treatment or cancer imaging, illustrate the impact of accelerators in
our current life. Today, accelerators use metallic cavities that sustain
electricfields with values limited to about 100 MV/m. Because of their ability
to support extreme accelerating gradients, the plasma medium has recently been
proposed for future cavity-like accelerating structures. This contribution
highlights the tremendous evolution of plasma accelerators driven by either
laser or particle beams that allow the production of high quality particle
beams with a degree of tunability and a set of parameters that make them very
pertinent for many applications.
