Most books on plastics machinery include a preamble on the origin of such equipment, and some even discuss the origin of plastic itself, dating back to the early 1900s and such men as Leo Baekeland - the real founder of synthetic plastics. There seems therefore, little pur­ pose in reiterating what has been said before and going over the same ground so adequately covered in a number of books as well as the trade press. We are indebted to the author of this excellent treatise on twin-screw extruders for getting right down to the business at hand. The author makes mention of two pioneers - Roberto Colombo and Carlo Pasquetti - who were the first to develop twin-screw ex­ truders. It was my good fortune to follow the work of these pioneers, and, interestingly enough, the principles were so good that their work continues to be relevant even to the advanced and more sophisticated models so well defmed in this book.