OBJECTIVE: The purpose of the Inclusive Indoor Play study was to learn about indoor play and develop design guidelines to inform design of inclusive playthings. PARTICIPANTS: Children with and without disabilities, parents, teachers, therapists, daycare owners and designers. METHODS: Focus group interviews: Children's drawings: and Indoor play simulation. RESULTS: The major findings suggest that: 1) play should encourage a child's creativity and develop imagination, 2) inclusive play concept must be employed to design playthings for children with wide age group, 3) inclusive designs improve usability, broaden market appeal, and increase user base, and 4) customizable playthings help children with and without disabilities personalize play situations. Three play principles provide new directions to designing inclusive playthings: 1) offer many play opportunities, 2) provide many modes of play, and 3) include many levels of play challenges. CONCLUSIONS: Inclusive Design Guidelines were developed from the findings of three studies: Focus group interviews, Children's drawings, and Play simulation. The guidelines served as useful tools for inclusive design and they were employed to design of six indoor playthings. The playthings were instrumental in promoting social inclusion and they met the criteria of the Inclusive Indoor Play project. (author abstract)