This book is an endeavor to provide a comprehensive overview of different methods of estimation of ocular biometry with their pros and cons, and various IOL power calculation formulae. The salient points of each chapter are reiterated in the form of easy-to-understand flowcharts and tables, to allow the readers to grasp the significant concepts and protocols at a glance. The book is divided into four sections sequentially covering the Evolution of IOL Power Calculation, Biometry, Present-day IOL Power Calculation Formulae and IOL Power Calculation in Challenging Situations. The highlight of this book is the section on challenging case scenarios, which will be of significant interest to all cataract surgeons, as it provides useful practical tips on how to obtain accurate biometry and which formula to use in each situation. Clinical case examples are provided at the end of each chapter with real-world case studies to further enhance understanding of the concepts. The book is intended to serve as a comprehensive guide for all Cataract Surgeons and will be an invaluable addition to their reading list. We hope the readers enjoy perusing the book and can integrate the practical aspects to enhance their decision-making skills and clinical practice.