The 40th annual Sanibel Symposium, organized by the faculty, students, and staff of the Quantum Theory Project of the University of Florida, was held on February 26–March 3, 2000. Again the Ponce de Leon Conference Center in St. Augustine, Florida was the site of the gathering of more than 300 scientists. The symposium followed the established format with plenary and poster sessions. A compact seven-day integrated program of quantum biology, quantum chemistry, and condensed matter physics provided for intense and lively cross-disciplinary interactions. The topics of the sessions covered by these proceedings include New Functionals and Formulations in DFT, Excited States and Currents in DFT, Nanoscale Materials and Materials by Design, Novel Processes at Surfaces and Interfaces, Quantum Dynamics of Extended Systems, Time-Dependent and Electronically Diabatic Phenomena, Density Matrix Applications, Progress in Electronic Structure Methods, Quantum Chemistry in Industry, Excited States and Photochemistry, Theoretical Inorganic Chemistry. A special nostalgia session “40 Years of Sanibel” included slides showing the original conference site at Casa Ybel on Sanibel Island and stories about “the old days.” The articles have been subjected to the ordinary refereeing procedures of The International Journal of Quantum Chemistry. The articles presented in the sessions on quantum biology and associated poster sessions are published in a separate volume of The International Journal of Quantum Chemistry. The organizers acknowledge the following sponsors for their support of the 2000 Sanibel Symposium: Army Research Office Grant #DAA 19-00-1-0020 “The views, opinions, and/or findings contained in this report are those of the author(s) and should not be construed as an official Department of the Army position, policy, or decision, unless so designated by other documentation.” The Office of Naval Research through Grant #N00014-001-0196 “This work relates to Department of the Navy Grant #N00014-001-0196 issued by the Office of Naval Research. The United States Government has the royalty-free license throughout the world in all copyrightable material contained herein.” DOE Grant #DE-FGO2-99ER25412 IBM Corporation HyperCube, Inc. The University of Florida Very special thanks go to the staff of the Quantum Theory Project of the University of Florida for handling the numerous administrative, clerical, and practical details. The organizers are proud to recognize the contributions of Mrs. Judy Parker, Ms. Coralu Clements, Ms. Cindy LePrell, Dr. Magnus Hedström, Mr. Mauricio Coutinho-Neto, and Mr. Kevin Shuford. All the graduate students of the Quantum Theory Project, who served as “gofers” are gratefully recognized for their contributions to the 2000 Sanibel Symposium.