Significant demands are being placed on the informal caregivers of chronically ill patients, including those suffering from cancer. Health care professionals need to be aware of these demands, and they need effective tools to assess the impact these demands place on the caregivers. Over the past 25 years, researchers have developed self-report instruments to assess informal caregivers. These instruments assess various aspects of the caregiving experience, including caregiver burden, needs, and quality of life. The purpose of this review was to identify and critically evaluate these instruments. MEDLINE and PUBMED were searched from 1966 to 2002. After an extensive literature search and review, and utilizing specific inclusion criteria, 28 instruments were identified and evaluated in terms of their development, content, and psychometric properties. In addition, a history of the construct and measurement development in the areas of caregiver burden, needs, and quality of life are discussed. Although some further development and refinement of instruments could benefit the field, depending on the questions researchers or clinicians seek to pursue, there are many proven tools available for their use. Future research needs to use these instruments to assess the effectiveness of interventions aimed at improving the care of the caregivers.