This work is intended to serve as an introduction to the principles and techniques used in the field of 2D-Quantitative Structure Activity Relationship (QSAR). Itlays foundation of certain information and skills that can be repeatedly employed in the field of computer added discovery of new lead and in the discovery of new drugs. A good introductory book of QSAR should contain (i) explain the fundamental concept in not too stilted language together with generous use of appropriate equation and diagrams; (ii) provide sufficient examples with detailed solution; (iii) present ideas in the smaller packages that are easily identified as part of a larger framework; and (iv) include tests and answers that enable the readers to evaluate their accomplishment. Some features have been built into this edition.