The Epsilon-proteobacterium Helicobacter pylori permanently inhabits the human stomach after acquisition. To thrive in this potentially hostile environment, H. pylori has undergone a substantial genome reduction in gene number and comparative genomics suggests H. pylori only encodes a limited set of protein secretion systems. In keeping with this limited protein secretion capability, H. pylori has also dispensed with components of the β-barrel assembly machinery. With a simplified means of delivering proteins into and across the outer membrane, how then does H. pylori target and assemble its outer membrane β-barrel proteins? To address this, we have used a range of bioinformatics and biochemical analyses to characterise the β -barrel assembly complex and the outer membrane proteome in H. pylori. This has revealed a reduced diversity in the actual β-barrel domain used in the vast majority of outer membrane proteins which is the specific feature recognised and folded by the BAM complex. The reduction of sequence diversity in β-barrel protein substrates is consistent with a simplification of the outer membrane biogenesis machinery.