The concepts of the laser-plasma based accelerator and injector are discussed here. The recent tests done at LOA as well as design studies of high-quality GeV electron beam production with low energy spread (1%) are presented. These laser-produced particle beams have a number of interesting properties and could lend themselves to applications in many fields, including medicine (radiotherapy), chemistry (radiolysis), and accelerator physics. They could be used as a source for the production of γ ray beams for nondestructive material inspection by radiography, or for future compact X-free electron laser machines.