Epithelial defense against infectious agents relies on the recognition of microbial products by pattern recognition receptors and the local production of antimicrobial peptides. This book provides a state-of-the-art overview of the basic characteristics and clinical relevance of antimicrobial peptides, with special emphasis on their role in skin, intestinal and lung inflammation. The evolutionary significance of antimicrobial peptides is highlighted by an in-depth analysis of their structure, activity and gene regulation in Drosophila melanogaster. Toll-like receptors are an important class of pattern recognition receptors, whose roles in recognizing bacterial molecular patterns and in the intracellular signalling pathways involved in the differentiation and function of dendritic cells are discussed. Finally, this book also addresses the role of intraepithelial lympho cytes in epithelial defense.