This book offers a comprehensive exploration of advanced molecular techniques used to study invertebrate innate immune reactions, focusing on both humoral and cellular-mediated responses. It delves into the intricate host-pathogen interactions and the surveillance mechanisms within hemocytes, providing a detailed understanding of invertebrate immunity. The chapters cover a range of topics, including cellular and humoral immunity, with detailed discussions on the microscopic examination of hemocytes and the roles of granulocytes, agranulocytes, and semigranulocytes. The book also examines the molecular-level interactions between host and pathogen, proteomic changes, and the structural-functional relationships of immune molecules. Critical attention is given to the impact of climate change on invertebrate immunity and its applications in aquaculture and the blue economy. The inclusion of flow charts, protocols, and vivid images enhances the readers curiosity and understanding of how these immune reactions can be studied using advanced molecular biology techniques. This book is an indispensable resource for immunologists, evolutionary biologists, and biotechnology professionals. It provides both foundational knowledge and cutting-edge research on invertebrate immunity, making it a must-read for anyone interested in the evolutionary origins and practical applications of innate immune systems. Researchers in the fields of immunology, evolutionary biology, and biotechnology will find this book particularly valuable, as it offers insights into the development of new therapeutics and the potential for invertebrate models in human studies.