The article discusses the control of adaptive immunity by the innate immune system, highlighting how it recognizes and responds to various pathogens. The innate immune system uses pattern-recognition receptors (PRRs) to detect conserved molecular patterns associated with different classes of microorganisms, such as bacterial and fungal cell-wall components and viral nucleic acids. These PRRs, including Toll-like receptors (TLRs), nucleotide-binding oligomerization domain (Nod)- and leucine-rich repeat-containing receptors (NLRs), RIG-I-like receptors (RLRs), C-type lectin receptors (CLRs), and AIM-2-like receptors, activate inflammatory responses and innate defenses. The recognition of pathogens by PRRs is followed by the induction of adaptive immune responses through specialized populations of dendritic cells (DCs). The article also explores the recognition of pathogens in different compartments, such as mucosal surfaces, skin, and blood, and the role of different DC subsets in generating specific T cell effector responses. It further discusses the costs associated with effector responses and the design principles of immune responses, emphasizing the two-tiered system involving sensors, lymphocytes, and effectors. Finally, it outlines future perspectives, including the exploration of new sensing pathways and the need to define the rules of engagement for protective immunity.The article discusses the control of adaptive immunity by the innate immune system, highlighting how it recognizes and responds to various pathogens. The innate immune system uses pattern-recognition receptors (PRRs) to detect conserved molecular patterns associated with different classes of microorganisms, such as bacterial and fungal cell-wall components and viral nucleic acids. These PRRs, including Toll-like receptors (TLRs), nucleotide-binding oligomerization domain (Nod)- and leucine-rich repeat-containing receptors (NLRs), RIG-I-like receptors (RLRs), C-type lectin receptors (CLRs), and AIM-2-like receptors, activate inflammatory responses and innate defenses. The recognition of pathogens by PRRs is followed by the induction of adaptive immune responses through specialized populations of dendritic cells (DCs). The article also explores the recognition of pathogens in different compartments, such as mucosal surfaces, skin, and blood, and the role of different DC subsets in generating specific T cell effector responses. It further discusses the costs associated with effector responses and the design principles of immune responses, emphasizing the two-tiered system involving sensors, lymphocytes, and effectors. Finally, it outlines future perspectives, including the exploration of new sensing pathways and the need to define the rules of engagement for protective immunity.