The assessment of disability including activities of daily living (ADL) is important as a clinical tool to document functional recovery as well as to assess the effectiveness of medical and rehabilitation interventions. Disability assessment is also important epidemiologically, in developing social policies, planning disability resources and in medical research and education. In this article, we review the definitions, history and advances in the field of disability assessment. We then describe the general principles of disability assessment in adults with a further detailed focus on six basic ADLs: feeding, bathing, dressing, toileting, transfers and mobility. We use a practical framework of an independent category and four dependent categories corresponding to an increasing level of assistance for each ADL. Finally we summarise the inherent problems and difficulties in disability assessment and emphasise the important role of rehabilitation in improving functional outcomes including the basic ADLs.