Epidemiology of CP aims to describe the frequency of the condition in a population and to monitor its changes over time. Also it studies the determinants of this condition which responsible for some changes over time. Classification of CP is an important step toward describing more homogenous subgroups of persons with CP. Several classifications exist based on neurological signs and topography, on motor function loss, on associated impairments, on severity of the clinical pattern and on the neuroimaging findings. Overall prevalence of CP is around 2 per 1000 live births in developed and in developing countries, with a trend toward a decrease during the last decade, at least for the more severe subgroups and the more tiny babies. Caution should be paid when interpreting changes in prevalence rates since factors that may influence these estimates are numerous.