In understanding the genetic architecture of plant resistance to insects, the magnitude or level of resistance can be qualitatively determined by analysis of standard scoring systems or quantitatively by establishment or development of insects. For pre-use genetic analysis, knowledge on the mechanisms of resistance is essential. This book narrates genetics of resistance involving different screening methods based on mechanisms of resistance through Quantitative Trait Loci (QTL) analysis for rice brown planthopper (BPH), Nilaparvata lugens. Genetic analysis through QTL mapping resulted in the identification of 7 putative and 16 probable QTLs associated with BPH resistance. The identified putative QTL were mapped to the following linkage groups: chromosome 1 (RZ276-RG146), chromosome 2 (RG157-RZ318), chromosome 6 (RG213-Est2), chromosome 6 (RG146-RG345), chromosome 6 (Pgi2-PRD10B), chromosome 7 (Est-RZ337B) and chromosome 7 (RG773-CD659). This book will provide basic concepts for studying the genetics of resistance in crop plants to insect pests and explore quantitative genetic nature of resistance to identify minor genes responsible for individual components of resistance.