Curli are proteinaceous fibers produced by many Enterobacteriaceae, particularly *Escherichia coli* and *Salmonella* spp., and are involved in various physiological and pathogenic processes. Curli fibers facilitate adhesion to surfaces, cell aggregation, and biofilm formation. They also mediate host cell adhesion and invasion, and induce inflammatory responses in hosts. The structure and biogenesis of curli are unique among bacterial fibers and belong to a class of fibers known as amyloids. Curli formation involves the secretion of the major subunit protein CsgA and its nucleation by CsgB, a process facilitated by the outer membrane protein CsgG. The regulation of curli gene expression is complex and influenced by various environmental cues, including temperature, nutrient availability, and oxygen tension. Curli are tightly regulated and play a crucial role in biofilm formation, which is a multi-step process involving reversible attachment, irreversible attachment, biofilm development, maturation, and dispersal. Curli are also important in the initial stages of infection, mediating attachment to host cells and interacting with host proteins. Additionally, curli are recognized by host immune system components, such as Toll-like receptors, leading to the activation of inflammatory cytokines. Curli represent a fascinating system for studying amyloid formation, protein secretion, and macromolecular assembly in bacteria.Curli are proteinaceous fibers produced by many Enterobacteriaceae, particularly *Escherichia coli* and *Salmonella* spp., and are involved in various physiological and pathogenic processes. Curli fibers facilitate adhesion to surfaces, cell aggregation, and biofilm formation. They also mediate host cell adhesion and invasion, and induce inflammatory responses in hosts. The structure and biogenesis of curli are unique among bacterial fibers and belong to a class of fibers known as amyloids. Curli formation involves the secretion of the major subunit protein CsgA and its nucleation by CsgB, a process facilitated by the outer membrane protein CsgG. The regulation of curli gene expression is complex and influenced by various environmental cues, including temperature, nutrient availability, and oxygen tension. Curli are tightly regulated and play a crucial role in biofilm formation, which is a multi-step process involving reversible attachment, irreversible attachment, biofilm development, maturation, and dispersal. Curli are also important in the initial stages of infection, mediating attachment to host cells and interacting with host proteins. Additionally, curli are recognized by host immune system components, such as Toll-like receptors, leading to the activation of inflammatory cytokines. Curli represent a fascinating system for studying amyloid formation, protein secretion, and macromolecular assembly in bacteria.