The recent and continuous development of powerful laser systems has permitted the emergence of new approaches for generating energetic electron beams. By focusing light pulses containing a few joules of energy in a few tens of femtoseconds onto gas jets, extremely large electric fields can be generated, reaching the terravolts per metre level. Such fields are 10 000 times greater than those produced in the radio-frequency cavities of conventional accelerators. As a result, the length over which electrons extracted from the target can be accelerated to hundreds of MeV is reduced to a few millimetres. The reduction of the size and the cost of laser-plasma accelerators is a promising consequence, but these electron beams also reveal original properties, which make them a wonderful tool for science. By adjusting the interaction parameters, the electron energy distribution can be tuned from a maxwellian-like distribution to a quasi-monoenergetic one. The new properties of these laser-based particle beams are well suited to many applications in different fields, including medicine (radiotherapy), chemistry (ultrafast radiolysis), material science (non-destructive material inspection using radiography) and, of course, for accelerator physics.