Monogenoideans are ectoparasitic, on the gills or skin of fishes. They exhibit both host and site specificity. They have highly specialized distinguished organs of attachment. The findings have been presented in the form of various sections in the present work, compiling morphology, seasonal aspects and statistical aspects. It has been drawn up to meet the requirements of students of different Indian and foreign universities. At the beginning of each section, a few introductory lines have been added in which the fundamental principles of that section have been discussed. The book begins with a comprehensive subject index that may be useful for quick searches. Reference citations within the body of the text adequately reflect the literature as subject is developed, which could be useful for further reading. A section begins with an abstract that enables a reader to know at the first glance the important points covered in that section. The present text is by no means a comprehensive account of the subject. In a work of this nature, sins of omissions and commissions are inevitable and for which I take full responsibility.