IVpili ( T4P) are bacterial virulence factors involved in a wide variety of functions including deoxyribonucleic acid uptake, surface attachment, biofilm formation and twitching motility. While T4Pare common surface appendages, the systems that assemble them and the regulation of their function differ between species. Pseudomonas aeruginosa, N eisseria spp.and M yxococcus xanthusare common model systems used to study T4Pbiology. This review focuses on recent advances in P . aeruginosa T4Pstructural biology, and the regulatory pathways controlling T4Pbiogenesis and function.