As a young ophthalmologist, I found corneal epithelial diseases a subject diffcult to grasp. One day, it occurred to me that the reason might be a lack of images showing the nature of the components of the changes visible with the slit lamp. With the slit lamp, the inevitable eye movements that blur the image limited the magnifcation level, but perhaps photography might be the answer. It was not a short journey, but in the end the idea proved right. By trial and error, the quality of the images improved, and after some time, I found that the resolution allowed reasonable comparisons with available images of histological preparations. Such comparisons allowed better und- standing of the substructures of epithelial in vivo lesions and, in conjunction with their in vivo dynamic features, eventually an understanding of at least some mechanisms behind them. This book, originating from over 20 years of experience with observations of ocular surface changes at high magnifcation level, covers several aspects of corneal epithelial lesions caused in humans by herpes simplex virus: various shapes of the lesions, their substructure and mechanisms behind them; morphological features of the healing p- cess, sequelae, complications, and some accompanying signs; and some rare cases. For those less familiar with the slit lamp image, I have added explanatory drawings to facilitate comprehension.