Innate immunity in crustaceans plays an important role in the cellular defense against pathogens. Crustaceans, including aquaculture species, such as shrimp, crabs, and crayfish, are highly susceptible to pathogens in the aquatic environment. The cellular innate immune system plays a central role in the life of most aquaculture crustaceans, and this chapter highlights some of the most important cellular components and pathways underlying their innate immune responses. Key cell types involved in innate immunity are discussed, focusing on hemocyte morphology and functional characteristics, supported by an illustration of shrimp immune responses. Hematopoietic tissues, the origin of immune cells, are examined for their role in hemocyte production and differentiation. The chapter goes deep into cellular innate immune sensing mechanisms, underlining pathogen recognition receptors, or PRRs: Toll-like receptors, Down syndrome cell adhesion molecules (DSCAM), and lipopolysaccharide and β-1,3-glucan binding proteins (LGBP and BGBP). Tables are provided here to present in detail the variations in Toll receptors and DSCAM in crustacean species. The signaling pathways Toll, IMD, and JAK/STAT are described, with tables summarizing the main components in shrimp, crabs, and crayfish. Important cellular immune effectors, including antimicrobial peptides (AMPs), are highlighted, and a comprehensive table summarizes AMPs identified in key crustacean species. The conclusion highlights the significance of cell immunity in crustaceans for improved disease management initiatives that contribute to improving aquaculture sustainability. This chapter provides a foundation for researchers and practitioners to enhance crustacean health through targeted immune modulation.