Perception of pathogen-associated molecular patterns (PAMPs) constitutes the first layer of plant innate immunity and is referred to as PAMP-triggered immunity (PTI). For a long time, part of the plant community was sceptical about the importance of PAMP perception in plants. Genetic and biochemical studies have recently identified pattern-recognition receptors (PRRs) involved in the perception of bacteria, fungi and oomycetes. Interestingly, some of the structural domains present in PRRs are similar in plants and animals, suggesting convergent evolution. Lack of PAMP perception leads to enhanced disease susceptibility, demonstrating the importance of PAMP perception for immunity against pathogens in vivo. Recently, proteins with known roles in development have been shown to control immediate PRR-signalling, revealing unexpected complexity in plant signalling. Although many PAMPs recognised by plants have been described and more are likely to be discovered, the number of PRRs known currently is limited. The study of PTI is still in its infancy but constitutes a highly active and competitive field of research. New PRRs and regulators are likely to be soon identified.