Cerebral palsy (CP) is a collection of disorders characterized by an insult to the developing brain that produces a physical disability as the primary or distinguishing feature. The spastic form of CP is most common and in those patients, additional clinical signs may include muscle shortening, diminished selective control, and weakness. The recognition of weakness as a component of CP has been longstanding as evidenced by the names given to this disorder and its subtypes. ‘Cerebral palsy’ means weakness originating from the brain, and the use of the suffixes ‘plegia’ or ‘paresis’ also indicate that weakness is a prominent feature. More than 50 years ago, Phelps contended that resisted exercise ‘to develop strength or skill in a weakened muscle or an impaired muscle group’ was an integral part of treatment in CP. (p 59) Since that time, physical educators have also advocated strengthening. Yet for years, conventional clinical wisdom in physical therapy argued against the use of strength testing and training in children with CP and, indeed, in all persons with CNS disorders. The rationale for this exclusion appears to be multifaceted. First, therapists were discouraged by the relatively meager functional responses to strength training in patients with spasticity compared with those with polio. Clinicians also feared that strong near maximal effort would exacerbate spasticity and muscle tightness in those who were already ‘stiffer’ than normal. Many also attested that impaired selective control in CP essentially prohibited performance of strengthening activities. Consequently, this approach was discarded in favor of a more direct focus on the brain. Only recently has strength testing and training experienced a resurgence in habilitation and rehabilitation programs for this population and for other spastic motor disorders. However, hesitation and even resistance to their incorporation are still encountered despite the lack of evidence to suggest that strengthening is detrimental in the presence of spasticity and accumulating evidence to support this type of exercise. The purpose of this annotation is to summarize existing research on strength testing and training, primarily focusing on CP and address the following clinical questions: (1) Can strength be measured reliably and in a valid way in cerebral palsy? (2) Is weakness a significant impairment in CP? (3) Is strength training effective in increasing force production and improving motor function and disability in CP? (4) Is strength training safe in the presence of spasticity and for children and adolescents, regardless of health status, who have an immature musculoskeletal system?