Rheumatoid arthritis (RA) disease activity plays a central role in causing disability both directly and via indirect effects mediated through joint damage, a major sequel of persistent active disease. Evaluation of RA disease activity is therefore important to predict the outcome and effectiveness of therapeutic interventions during follow-up. However, disease activity assessment is among the greatest challenges in the care of patients with RA. We regard measurement of activity as an essential element of following the fate of joint diseases like RA. This evaluation can be facilitated by the use of reduced joint counts and simple indices, such as the Simplified Disease Activity Index (SDAI) and the Clinical Disease Activity Index (CDAI). These scores are validated outcomes for RA and allow the assessment of: actual disease activity, response to therapy, and achievement of particular states such as remission. The simplicity of these scores enables patients to understand the level of their disease activity, as assessed by the rheumatologist, and to correlate increments and decrements of disease activity directly with all aspects of the disease.