The Wage Structure Survey comprise two operations, one with a four-year periodicity and another annually, which complements the results of the first for the years in which this is not carried out.

The Cuatrienial Wage Structure Survey is a statistical operation carried out since 1995 within the framework of the European Union with common criteria of methodology and content, in order to obtain comparable results on the structure and distribution of wages among its Member States. The survey investigates the distribution of wages based on a wide variety of variables such as sex, occupation, branch of activity, seniority, or company size.

The Annal Wage Structure Survey has been carried out since 2004 providing estimates of gross annual earnings per worker classified by type of working day, sex, economic activity and occupation. As the annual survey is not carried out in the years in which the quadrennial survey is carried out, to facilitate the publication of time series, since 2006 the information for these years is completed by incorporating the same tables that are prepared for the rest of years using the information from of the quadrennial survey.

In both surveys, the information is obtained from the joint exploitation of files from the Social Security (SS) and the Tax Agency, together with the use of a specific questionnaire.