Innate immunity in invertebrates represents the first line of defense against invading pathogens. The host’s response to invading pathogens is a vital physiological reaction across all living organisms, and various defense mechanisms have evolved to preserve cellular integrity, homeostasis, and survival. Invertebrates possess cellular receptors that bind to foreign elements, enabling them to distinguish between self and non-self. In multicellular animals, this function is linked to phagocytes—known by different names like amebocytes, hemocytes, and coelomocytes—in diverse groups of invertebrates. These phagocytes are equipped with pathogen recognition receptors (PRRs) that detect pathogen-associated molecular patterns (PAMPs), which are conserved across various pathogens such as viruses, bacteria, fungi, protozoans, and helminths. Prominent PRRs include Toll-like receptors (TLRs), Nod-like receptors (NLRs), and scavenger receptors. Upon binding to a pathogen, these receptors trigger a cascade of cellular reactions that lead to the production of effector molecules. Cytokines are crucial in coordinating these responses, even in lower invertebrates, ultimately leading to the removal of the pathogen. The key effector molecules include reactive oxygen and nitrogen species, antimicrobial peptides, lectins, fibrinogen-related peptides, leucine-rich repeats (LRRs), and complement-related proteins. Antimicrobial peptides (AMPs) are crucial to invertebrate defense as they can penetrate microbial pathogens membranes, causing cell death and effectively preventing infections. In this chapter, we explore the immune mechanisms of invertebrates, which differ significantly in their modes of action. We aim to understand how these mechanisms function and investigate whether they can be harnessed to benefit agriculture or combat pathogens.