Dimensional analysis is a simple and intuitive method for determining the functional dependence of physical quantities relevant to a certain process. In other words, it is one of the powerful, widely applicable theoretical tools to reduce a complex physical system to a simpler form before their quantitative analysis or experimental investigations. This book (containing 10 chapters) attempts to provide a basic understanding of various problems in science through dimensional analysis (DA). There are some uncommon and interesting problems which have been attempted by DA. DA also can be helpful to obtain some scaling relation without solving the differential equation. DA has been applied suitably to discuss some quantum mechanical bound state and astrophysics problems that are not often highlighted in a text book. A chapter has been devoted to discuss the breakdown of this method to classic problems in physics. This book is suitable for Under Graduate Students, Post Graduate Students and Researchers in Natural Sciences. We have included 200 exercises and 200 multiple choice questions (MCQ) for the students to test their understanding and motivate them to pursue estimation and modeling.