In October 1998 a conference was held in Lisbon to celebrate Ludwig Streit's 60th birthday. This book collects some of the papers presented at the conference as well as other essays contributed by the many friends and collaborators who wanted to honor Ludwig Streit's scientific career and personality. The contributions cover many aspects of contemporary mathematical physics. Of particular importance are new results on infinite-dimensional stochastic analysis and its applications to a wide range of physical domains. List of Contributors: S Albeverio, T Hida, L Accardi, I Ya Aref'eva, I V Volovich; A Daletskii, Y Kondratiev, W Karwowski, N Asai, I Kubo, H-H Kuo, J Beckers, Ph Blanchard, G F Dell'Antonio, D Gandolfo, M Sirugue-Collin, A Bohm, H Kaldass, D Bollé, G Jongen, G M Shim, J Bornales, C C Bernido, M V Carpio-Bernido, G Burdet, Ph Combe, H Nencka, P Cartier, C DeWitt-Morette, H Ezawa, K Nakamura, K Watanabe, Y Yamanaka, R Figari, F Gesztesy, H Holden, R Gielerak, G A Goldin, Z Haba, M-O Hongler, Y Hu, B Oksendal, A Sulem, J R Klauder, C B Lang, V I Man'ko, H Ouerdiane, J Potthoff, E Smajlovic, M Röckner, E Scacciatelli, J L Silva, J Stochel, F H Szafraniec, L Vázquez, D N Kozakevich, S Jiménez, V R Vieira, P D Sacramento, R Vilela Mendes, D Volný, P Samek. Contents:Some Themes of the Scientific Work of Ludwig Streit (S Albeverio)Nonlinear Lie Algebras in Quantum Physics and Their Interest in Quantum Field Theory (J Beckers)Rigged Hilbert Space Resonances and Time Asymmetric Quantum Mechanics (A Bohm & H Kaldass)The Relativistic Aharonov-Bohm-Coulomb Problem: A Path Integral Solution (J Bornales et al.)Time Dependent and Nonlinear Point Interactions (R Figari)Stochastic Processes and the Feynman Integral (Z Haba)Nonrenormalizability and Nontriviality (J R Klauder)On the Spectrum of Lattice Dirac Operators (C B Lang)External and Internal Geometry on Configuration Spaces (J L Silva)Spinor Description of a General Spin-J System (V R Vieira & P D Sacramento)and other papers Readership: Theoretical physicists, mathematical physicists, mathematicians, computer scientists and economists. Keywords: