We are at the beginning of the third decade of studies at the molecular level on the pathogenesis of Listeria monocytogenes and the response of the host to its infections. It is a good time to survey the wealth of information that these studies have revealed and to think about perspectives for a more complete understanding of this important pathogen. During the past 20 years, L. mono- togenes has emerged from relative obscurity to being one of the most intensely studied bacterial pathogens. In the opening chapter, Daniel A. Portnoy provides a personal and historical account of the development of our understanding at the molecular level of invasion of the host cell, growth in the cytosol, and ce- to-cell spread by means of actin polymerization-powered motility. We are also fortunate to have contributions from Pascale Cossart and Werner Goebel and their colleagues. These pioneering investigators continue to make major cont- butions to the molecular description of almost every aspect of L. monocytogenes pathogenesis. All chapters in this book have been written by experts who have contributed widely to this field. We are extremely grateful for the efforts of all contributors who have provided contemporary accounts of the status of various aspects of L. monocytogenes pathogenesis and the host response. Their positive responses to this effort are deeply appreciated. Any specialist volume in the biological sciences can only provide a snapshot of the field at the time of its publication.