In Volume IV, the focus lies on Rembrandt's self-portraits. During this research it became obvious that matters of authenticity cannot be viewed separately from questions relating to the original function and meaning of these works. Rembrandt's intriguing life-long practice of portraying himself in front of a mirror is examined in depth in this volume. As a result, not only has the group of approximately forty painted self-portraits gained transparency, but also new insights have been developed regarding Rembrandt's drawn and etched self-portraits. The problems of authenticity relating to a substantial number of self-portraits which in the past were attributed to Rembrandt, in this volume receive an unexpected nuance: through a combination of technical and stylistic research it is demonstrated that some of Rembrandt's self-portraits were in fact painted by others in his workshop. In clear and accessible explanatory texts the different paintings are discussed. Among the many illustrations are life-size colour reproductions of the faces of the self-portraits under discussion. Details are shown where possible, as well as the results of modern day technical imaging like X-radiography. The volume contains an - in several respects eye-opening - essay by the head of the Rembrandt Research Project, Ernst van de Wetering, on the problems of authenticity and function of Rembrandt's self-portraits. In addition, the book includes groundbreaking contributions by Marieke den Winkel on the meaning of dress and costume in Rembrandt's self-portraits, by Karin Groen on the use of grounds in Rembrandt's workshop and in paintings by his contemporaries, and a study by Jaap van der Veen concerning 17th-century ideas about authenticity in art. This reference work should be part of every serious art historical institute, university or museum. The enigma of Rembrandt's self-portraits, one of the most compelling phenomena in art history has been unravelled by Ernst van de Wetering with unprecedented thoroughness.