This special issue contains 26 articles, selected from 98 scientific papers presented at the Third International Working Conference on Biosignal Interpretation (BSI99), which was successfully held in Chicago from June 12-14, 1999. The BSI99 Working Conference is a joint initiative of IFMBE, IMIA, and IEEE-EMBS, bringing together engineers and scientists to discuss the recent advances in the field of biosignal interpretation. This Working Conference aims to explore the relatively new field of biosignal interpretation including model-based biosignal analysis, their interpretation and integration, and to extend existing signal processing technology for the effective utilization of biosignals in a practical environment and a deeper understanding of biological functions.