The Work Ability Index? is a work ability evaluation method developed by the Finnish Institute of Occupational Health for use in health examinations. Its functionality has been tested at both the national and international levels. This instruction booklet contains information regarding - the background questions of the Work Ability Index? questionnaire - the questionnaire itself - how to evaluate scores - suggested measures to be undertaken on the basis of the scores obtained from the Work Ability Index? questionnaire, and - directions regarding data security questions which must be taken into consideration when using the questionnaire. The Work Ability Index? has been developed mainly for use by occupational health services as part of health examinations to monitor work ability and evaluate the need for treatment or rehabilitation.