We outline a theory for the calculation of the laser beam quality factor of an aberrated laser beam. We provide closed
form equations which show that the beam quality factor of an aberrated Gaussian beam depends on all primary
aberrations except tilt, defocus and x-astigmatism. The model is verified experimentally by implementing aberrations as
digital holograms in the laboratory. We extend this concept to defining the mean focal length of an aberrated lens, and
show how this definition may be of use in controlling thermal aberrations in laser resonators. Finally, we look at
aberration correction and control using a combination of spatial light modulators and adaptive mirrors.