This article describes contents and major results of the project SIESTA (BIOMED-2) supported by the European Commission. The main aim was intensive research on the architecture of human sleep and the development and evaluation of new methods for analysing sleep based on polygraphic recordings, mainly EEG. In this connection, alternatives to the rules set up by Rechtschaffen and Kales for the description of human sleep were investigated. The project SIESTA yielded two essential results: first of all, the model and the development of an automatic sleep analyser for polygraphic recordings with a time resolution up to 1 s. Validation of the results of the analyser is still in progress and reveals possibilities for adaptation and further development. Secondly, an essential result was setting up a normative database for polygraphic sleep recordings and additional subjective and objective parameters. The database contains data of 295 subjects each with two sleep recordings. The age distribution of 198 healthy subjects ranges from 20 to 90 years with an approximately equal distribution across the decades. Furthermore, the database comprises data of 97 patients.