This volume is a collection of papers presented at the Twelfth International Conference on Ultrafast Phenomena held at Charleston, SC, from July 9 to 13, 2000. The Ultrafast Phenomena Conferences are held every two years and provide a forum for discussion of the latest results in ultrafast optics and their applications in science and engineering. A total of more than 200 papers was presented, reporting progress in the technology of generating and characterizing ultrashort pulses, including new techniques for shortening the duration of laser pulses, for stabilizing their absolute phase, and for improving tunability over broad wavelength ranges, output powers and peak intensities. Ultrafast spectroscopy, including techniques like time-resolved X-ray diffrac- tion and two-dimensional spectroscopy, continues to give new insights into fundamental processes in physics, chemistry and biology. Control and opti- mization of the outcome of ultrafast processes represent another important field of research. There is an increasing number of applications of ultrafast techniques, for instance in material diagnostics and processing and in imag- ing and microscopy. The enthusiasm of the participants, among them many students, the high quality of the papers and the nice conference site made the conference successful and pleasant.