It is well known that a fraction of defects produced during irradiation accumulate in crystalline solids in the form of clusters of self-interstitial atoms (SIAs) and vacancies, loops, tetrahedra, dislocation segments and cavities. The irradiation parameters such as recoil energy, damage rate, helium production rate and the production rate of transmutant impurities may affect the rate and the magnitude of the damage accumulation. Possible mechanisms by which these parameters may affect the damage accumulation are described. Specific examples are given to illustrate the fact that the recoil energy plays a significant role in determining the magnitude of the damage accumulation. Unfortunately, the available experimental results are not sufficient to allow an unambiguous identification of the mechanisms involved in the evolution of the damage accumulation. Some suggestions are made for carrying out simple, clean and specifically designed experiments to identify the role of irradiation parameters in defect production and accumulation.