It is a pleasure to present this introduction to a very special issue of Translational Andrology and Urology ( TAU ) that is focused on “testosterone replacement therapy” (TRT). As editors, we strove to present a current, state-of-the-art and global perspective on this very common and important medical condition. Established national and international experts as well as rising stars were invited to contribute and the response to our invitations to provide manuscripts on this timely subject has been overwhelming and allowed for the inclusion of numerous outstanding original articles, comprehensive review articles, as well as important opinions from many of the world leaders in the area of andrology. The papers in this issue of the TAU journal provide insightful updates and perspectives on our current understanding of the epidemiology, pathophysiology and important role of TRT in clinical practice.