The 5th edition of Cardiac Surgery in the Adult is dedicated to Dr. Lawrence Cohn, Emeritus Chief of the Division of Cardiac Surgery at Brigham and Women's Hospital and Virginia and James Hubbard Professor of Cardiac Surgery at Harvard Medical School, who sadly passed away unexpectedly during the final stages of preparation of this latest edition of “his” reference textbook. Dr. Cohn leaves a legacy of excellence seldom seen in academic surgery, and he will be sorely missed by all of us who knew him, and especially those of us lucky enough to have been mentored by him. Dr. Cohn received his training in cardiothoracic surgery under the tutelage of Dr. Norman Shumway at Stanford University, and after completing his fellowship in 1971 he joined the staff of the Peter Bent Brigham Hospital in Boston. Over the next 45 years he was the driving force behind the success of the Harvard program, and became the Chief of the Division of Cardiac Surgery in 1986. A clinical cardiac surgeon first and foremost, Dr. Cohn performed over 11,000 open heart procedures during his career, and was best known for his pioneering and international leadership in minimally invasive valve surgery. His academic contributions included over 500 peer-reviewed publications, 100 book chapters, and 750 invited lectures on virtually all topics in cardiac surgery, but perhaps his greatest academic legacy was his editorship of the 2nd, 3rd, and 4th editions of Cardiac Surgery in the Adult, which under his vision became the most widely referenced international textbook in adult cardiac surgery. During his career Dr. Cohn earned the highest awards and honors a cardiac surgeon could possibly achieve, serving as the 79th President of the American Association for Thoracic Surgery, receiving an honorary Masters of Medicine from Harvard, and receiving the American Heart Association's Paul Dudley White Award, among numerous others. He would claim his greatest honor, however, was the opportunity to train over 200 residents and fellows from all over the world, many of whom went on to become Division Chiefs, Department Chairs, and leaders in the specialty. His American Association for Thoracic Surgery presidential address “What the Cardiothoracic Surgeon of the 21st Century Ought to Be” personifies the essence of what made him one of the masters of cardiac surgery who will be remembered by generations to come. Through leadership by example in all phases of his career, his unwavering commitment to the individual patient was the foundation of all of his accomplishments, and few surgeons have had such a profound impact on our specialty. Dr. Cohn was my teacher, mentor, and friend, and it was an honor to be asked by his wife of 55 years, Roberta, to assume the role of Co-Editor to complete this 5th edition of his textbook. Dr. Cohn left footprints too large to fill, but with the help of the many authors who contributed chapters and the publisher's leadership, we now present this peer tribute to one of the greatest cardiac surgeons of all time.