Brassica napus (rapeseed) is a vital oilseed crop globally, but its productivity is severely affected by biotic stresses, including fungal, bacterial, and viral pathogens, as well as insect pests. This chapter explores the mechanisms of biotic stress resistance in B. napus, focusing on innate immunity, biochemical responses, and structural defenses. The genetic basis of resistance, including quantitative trait loci (QTL) mapping and biotechnological approaches such as RNA interference (RNAi) and genetic engineering, is discussed. Additionally, environmental management strategies, including crop rotation and microbial applications, are highlighted. Recent advances in multi-omics, nanotechnology, and microRNA-mediated resistance are also reviewed. Integrating traditional breeding with modern genomic tools offers promising avenues for developing disease-resistant B. napus varieties, ensuring sustainable crop production in the face of emerging biotic challenges.