Inertial confinement fusion (ICF) is based on implosion of spherical shells. Intense laser beam ablation of the shell's outer surface creates the rocket reaction providing the momentum of the implosion. This same ablation instantly creates an outwardly moving plasma, within which the laser beam must propagate. The intense laser beam can create a variety of secondary processes in this plasma. Some of these processes can be deleterious to the efficiency of the implosion: diverting the laser energy, disturbing the symmetry of the convergence, or prematurely heating the imploding fuel. Laser-plasma interaction physics is the study of these secondary processes. Considerable experimental evidence has been accumulated, and many more observation techniques are being developed, showing the onset of these phenomena. The challenge is to relate the experimental evidence and the theories, so as to reliably predict the behavior of future reactor pellet implosions. Interest is not confined to ICF application. Because of their ability to support longitudinal electric fields in excess of 1 GeV/cm, laser-produced plasmas have been incorporated in two types of experimental particle accelerators. One is the beat-wave accelerator, and the other is the wake-field accelerator. Much experimental study and theoretical analysis remain to be done.