This paper begins by looking at musical aptitude. It identifies research that compared the musical aptitude of people with, and without, an intellectual disability, and investigations that assessed the musical aptitude of diagnostic subgroups from within the intellectual disability population (Down syndrome, musical savants, autistic spectrum disorder, Williams syndrome). This paper then goes on to consider research that examined how individuals with an intellectual disability responded to active (improvisation, and Music Activity Therapy) and receptive (contingent, contingent-interrupted, and non-contingent music) interventions. The studies are ordered according to therapeutic outcome, and it describes their method, and considers various issues that arose. The conclusion summarises the strengths and weaknesses of the experimental writing, and identifies agendas for music therapy research with this population. It argues that the experimental research should not be considered in isolation. Instead, it suggests, that along with the descriptive writing (discussed in part one of the review), the experimental writing is part of a body of work that captures both the richness of clinical experiences, and the cause-effect relationships underlying those experiences.