In 1996, we organized a workshop, inter alia, at the National Research Co- cil in Milan under the generous sponsorship of the European Science Foun- tion. On that occasion, a small group of investigators convened from many countries and presented early evidence of the possibility of assembling basic units of mammalian chromosomes into artificial constructs (or, indeed, red- ing the relevant components to more manageable dimensions and defined c- stitution). Progress in the following years has been slow but steady. Many scientists who took part in the workshop have since been engaged in active and prod- tive research. It goes to the credit of Humana Press to have realized the need for a book on artificial chromosomes that aims to provide better tools to all scientists committed to this field who are confronted with very difficult tech- cal problems. We have strived to cover in Mammalian Artificial Chromosomes: Methods and Prools all relevant areas of artificial chromosome research, from basic genetics to daring attempts to build new tools for genetic therapy. We are of course grateful to the authors who have accepted the task of describing the technical steps and pitfalls that can be encountered in their research. Rarely has a very delicate methodology been presented with such meticulous care. We have been helped in this enterprise by the excellent librarian of the LITA Institute in Segrate, Italy, Ms. Claudia Piergigli, whom we thank warmly. Ms.