Ernst Abbes theory of image formation in the microscope This book is an English translation of Die Lehre von der Bildentstehung im Mikroskop von Ernst Abbe with annotations and other added material. The original German edition was published in 1910 and was an expanded version of the lectures given by Ernst Abbe in 1887. The original book is the only publication giving a detailed account of Abbes theory of image formation in the microscope. Chapter 1 introduces geometrical optics. Chapter 2 discusses theory of image formation based on optical diffraction. Chapter 3 deals with optical images of several kinds of objects being illuminated on and off axis. One example is the off axis illumination for improving the resolution of two neighboring slits; another example is a (pi) phase edge in the middle of an otherwise transparent slit giving zero light intensity there in its image. The chapter also introduces coherent imaging as two back to back diffraction processes and discusses the resolution limit of an imaging system. The book concludes with Chapter 4 on the effect of artificial blocking of certain diffraction orders on the final image