123 Copyright © 2015, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited. Chapter 4 DOI: 10.4018/978-1-4666-8136-1.ch004 ABSTRACT Developing efective structure-activity/property/toxicity relationships (QSAR/QSPR/QSTR) is very help- ful in predicting biological activity, property, and toxicity of a given set of molecules. Regular change in these properties with the structural alteration is the main reason to obtain QSAR/QSPR/QSTR models. The advancement in making diferent QSAR/QSPR/QSTR models to describe activity, property, and toxicity of various groups of molecules is reviewed in this chapter. The successful implementation of Conceptual Density Functional Theory (CDFT)-based global as well as local reactivity descriptors in modeling efective QSAR/QSPR/QSTR is highlighted. 1. INTRODUCTION The properties of molecules mainly depend on the distribution of electron density within the individual molecules. It is, therefore, believed that molecules having similar structures will exhibit similar proper- ties. On this hypothesis, the idea of structure-activity relationship (SAR) exists (Nantasenamat et al., 2009). Accordingly, it is assumed that molecules with similar structures exhibit comparable activities (properties), and, so on the basis of known properties of a set of molecules, prediction of the properties of unknown molecules having similar structures could be made, provided appropriate models are de- Quantitative Structure-Activity/ Property/Toxicity Relationships through Conceptual Density Functional Theory-Based Reactivity Descriptors Sudip Pan Indian Institute of Technology Kharagpur, India Ashutosh Gupta Udai Pratap Autonomous College, India Venkatesan Subramanian Central Leather Research Institute, India Pratim K. Chattaraj Indian Institute of Technology Kharagpur, India