Multicellular organisms continually come into contact with microbes in the environment, and protecting themselves from infection is vital to their survival. The innate immune system has a critically important role in acting as a first line of defence against this threat, by rapidly detecting and destroying any foreign invaders. Recognition of pathogens by the innate immune system is achieved through the actions of a large collection of pattern recognition receptors that bind to unique features of pathogens called pathogen‐associated molecular patterns that are not normally found in the host. Recognition is followed by the production of cytokines and chemokines and activation of innate immune responses that restrict, destroy and dispose of the pathogen and promote the subsequent activation of an adaptive immune response. Key Concepts Pattern recognition receptors (PRRs) detect foreign molecules associated with pathogens, termed pathogen‐associated molecular patterns (PAMPs). PAMPs are specific to groups of pathogens and are not normally found in the host. PRRs are found in different tissues and in different subcellular compartments according to the types of pathogen that they recognise. Activation of PRRs leads to innate immune responses that destroy the pathogen.