This paper reviews the methods and principles for quality of life assessment. The aging of the population and the improved survival of people with acute and chronic conditions have produced several levels of disability requiring long-term treatment and rehabilitation. In 1948 the World Health Organization defined health as not merely the absence of disease but rather a state of complete physical, mental, and social well being. This term evolved from its conceptual definition to the development of scales to measure the quality of life beyond physical status. Thus, quality of life assessment includes areas such as mental health, social support, and life satisfaction. It is recognized that the expectations, vitality, pain, disability, and personal experiences influence the perception of a person's general health. A composite measurement aimed to quantify health according to physical, mental, and social well being simultaneously would likely find people at different points on the three different continua, but in the midranges of the composite. The multidimensionality problems and the level of subjectivity involved in the assessment of the quality of life require valid and reliable instruments. This paper present an inventory of 126 questionnaires aimed to measure the quality of life for several diseases and populations. A better understanding of the methods to assess the quality of life will allow the incorporation of these instruments in the comprehensive assessment of patients, into clinical trials, and for health services research. The English version of this paper is available at: http://www.insp.mx/salud/index.html.