This chapter addresses the delicate transition from cerebral palsy (CP) neurological diagnosis to its functional prognosis. While the first one explores the lesion, essentially what has been compromised, the second one questions what can still be achieved by exploiting what has been saved (conserved) and can resume functioning, albeit in a different way. There is no direct relationship between lesion and palsy, because palsy is not the consequence of the lesion, but the different way of functioning of the entire CNS. Rehabilitation aimed at the lesion should theoretically take into account the injury etiology; that aimed at the structure should be able to generate normality; that aimed at the function can instead produce only adaptivity, and for this reason, it should allow compensation and substitutions. If diagnosis is a look at the past, prognosis is a possible hypothesis about the future. CP rehabilitation is based on prognosis, i.e., the possibility of modifying for better functions produced by the child’s nervous system, despite the nonamendable presence of the lesion. Results should not be aimed at rebuilding normality, but adaptivity (a performance good enough for that task, of that person, in that context, at that moment). Rehabilitation is effective where the treated function is modifiable (plasticity), the child is able to learn alternative strategies, is motivated and committed to solving problems that development progressively presents. Palsy represents, in a positive way, the attempt of CP children to face the needs that development gradually imposes on them and therefore acquires an evolutionary dimension (development of palsy rather than palsy of development). While the confronted “problems” remain the same, the adopted “solutions” can differ from child to child. Function stops developing when it becomes “good enough” to satisfy the needs that generated it (competence). The level of function is also influenced by the formal rules that society requires each of us to respect (contextuality) and by personal evaluations (consonance) due to the image of ability that we intend to convey to others.