Historical documents, medical and non-medical, and portraits are full of descriptions of children and adults, whose posture and movement resembled what we now call typical of persons with cerebral palsy. This chapter briefly recalls that in the nineteenth and especially in the twentieth century, thanks to the contribution of many neurologists and orthopedic surgeons, a medical definition of several palsies was published (Bax MCO, Dev Med Child Neurol Dev Med Child Neurol; 6:295307, 1964) that lasted for decades. However, its limitations gradually emerged (difficulty of tracing the borders between cerebral palsy and other early-onset motor disorders, the exclusion in the definition of non-motor symptoms in CP…). This led to the new definition of cerebral palsy (Rosenbaum P, Paneth N, Leviton A et al., Dev Med Child Neurol, 109:8–14, 2007) that is now generally applied, but it still has limitations and revisions are suggested. The chapter also includes an overview of the historical models to classify cerebral palsy, mainly based on the topography of posture and movement disorders and on the main neurological features. The limitations of these models are reported and new perspectives are shortly mentioned that are fully described in the following chapters.