The Fourth Congress of the International Society for Analysis, its Applications and Computation (ISAAC) was held at York University from August 11, 2003 to August 16, 2003. It was supported by the Academic Initiative Fund of the Faculty of Arts, NSERC grants from some members of the Department of Mathematics and Statistics and the Office of the Vice-President Academic of York University. In spite of two SARS outbreaks in Toronto in 2003, the ISAAC Congress was held as scheduled and was well attended by mathematicians from all over the world. There were nine plenary lectures and seventeen...

As a satellite conference to the Fourth Congress of European Mathematics held at StockholmUniversityin2004, theInternationalConferenceonPseudo-Di?erential Operators and Related Topics was held at V] axjo ] University in Sweden from June 22 to June 25, 2004. The conferencewas supported by Vaxj ] oU ] niversity, theFIRB Research Group on Microlocal Analysis of Universit a di Torino, and the Int- national Society for Analysis, its Applications and Computation (ISAAC). The conferencewas well attended by about 50 mathematicians fromBulgaria, Canada, Denmark, England, Finland, Germany, Italy,...

This volume consists of the plenary lectures and invited talks in the special session on pseudo-differential operators given at the Fourth Congress of the International Society for Analysis, Applications and Computation (ISAAC) held at York University in Toronto, August 11-16, 2003. The theme is to look at pseudo-differential operators in a very general sense and to report recent advances in a broad spectrum of topics, such as pde, quantization, filters and localization operators, modulation spaces, and numerical experiments in wavelet transforms and orthonormal wavelet bases.