Rheumatoid arthritis (RA) is the most common systemic inflammatory joint disease. It can be treated effectively with disease modifying antirheumatic drugs, and the currently propagated treatment strategy is to treat RA consequently, and revise the therapeutic approach frequently on the basis of proper disease activity evaluation. In the current review, we focus on the instruments and measures used in the assessment of RA disease activity. We will first consider the so-called core set measures of activity, prividing comprehensive overviews on joint count scales, global scales, pain scales, biomarkers, and functional assessment instruments. The second part of the review focuses on the value of composite measures of disease activity; a term under which we subsume activity indices using various formulae, self-assessment tools of disease activity, and response criteria. Among the inflammatory rheumatic diseases, RA is the one for which the most intensive research is done, and usually instruments that work for RA are further tested for other joint diseases. However, there is still a research agenda for the assessment of disease activity, even for RA. One important aspect is to assess the reliability and utility of all available instruments, including the very low end of disease activity, since remission has become an achievable goal. Another focus of disease activity assessment is to derive measures that work in clinical trials and in daily practice, but are also well understood by patients and physicians. This will further improve our ability to care for patients with RA consequently.