It is increasingly necessary to have a measuring instrument available in the health field that can be used in clinical practice and research. In order to guarantee the quality of their measurements it is essential that the instruments should be subjected to a process of validation. This process consists in adapting the instrument culturally to the setting where its psychometric characteristics are to be administered and checked, such as: reliability, validity, sensitivity and feasibility. There are measuring instruments from the health field available in other languages but that have not been validated into Spanish. Besides, the methodology for validating an instrument is little understood by the health professionals, which explains the indiscriminate use of instruments that have only been adapted or validated in a way that is not very consistent. The aim of this review is to bring up to date the process of validating an instrument for measuring health, and what it involves, in a practical way. The accessibility of evaluation instruments that have been culturally adapted and validated in different languages will facilitate the comparison of results obtained with the same instrument and the development international studies in different cultures.