INTRODUCTION Interdisciplinary differences regarding understanding the International Classification of Functioning, Disability and Health (ICF) concepts activity/participation may hinder its unifying purpose. In the ICF model, functioning (and disability) is described as a tripartite concept: 1) Body structures/functions, 2) Activities, and 3) Participation. Activities refer to an individual perspective on disability that does not tally with the basic structure of social models. OBJECTIVE To review how activity and participation are actually used in studies of intellectual disability (ID). CONCLUSION Based on 16 papers, four different usages of activity/participation were found. 1) Theoretical reference to tripartite ICF concept with attempts to use it. 2) Theoretical reference to tripartite ICF concept without actual use of activities. 3) "Atheoretical" approach with implicit focus on participation. 4) Theoretical reference to bipartite concept with corresponding use of terms. The highlighted studies have in common a focus on participation. However, the usage of the term "activity" differs both within and between studies. Such terminology will probably confuse interdisciplinary communication rather than facilitating it. Also, the use of an explicit underlying theory differs, from references to a tripartite to references to a bipartite concept of disability. This paper is focused on ID, but the discussed principles regarding the ICF and interdisciplinary disability theory are applicable to other diagnostic groups within rehabilitation practices.