Gram-negative bacteria, such as Escherichia coli, contain four distinct cellular compartments: the cytoplasm, the inner membrane, the periplasm, and the outer membrane. All of the protein and lipid components of these compartments are synthesized in the cytoplasm or at the periplasmic face of the inner membrane. As a consequence of this, cellular components that are destined for extracytoplasmic locations, such as the periplasm and outer membrane, must be properly targeted to their respective locations. Studies presented in this thesis focus on the targeting and assembly of outer membrane b-barrel proteins in Escherichia coli. A major goal of this work was to understand the mechanism by which outer membrane proteins travel through the periplasm, and interact with the assembly site in the outer membrane. The process of protein transport through the periplasm has remained mysterious and controversial. The favored model for the transport of outer membrane proteins to the outer membrane states that unfolded outer membrane proteins interact with chaperones and folding factors in the periplasm as they emerge from the inner membrane translocation machinery. Indeed, various periplasmic chaperones, such as Skp, SurA, and DegP, have been implicated in outer membrane protein biogenesis. Synthetic lethal phenotypes were observed for null mutations in skp and surA and for null mutations in degP and surA, but not for skp and degP. Based on these observations, a model for parallel pathways for chaperone activity was proposed: Skp and DegP function in one pathway, while SurA acts in a separate, parallel pathway. Here, we clarify the relationship between these three chaperones and gain insight into the mechanism of outer membrane protein biogenesis using depletion analysis. We show that the depletion of redundant periplasmic chaperones leads to the accumulation of misfolded outer membrane proteins. Depletion of SurA results in a decrease in outer membrane density, while the loss of DegP and Skp have no effect on outer membrane density. Based on these and other results, we suggest that SurA is the primary chaperone for the bulk mass of outer membrane proteins escorting proteins from one side of the periplasm to the other, while DegP/Skp plays more of a secondary role that is important at times of stress. SurA delivers outer membrane proteins to the YaeT complex, which is responsible for their assembly. This complex contains the outer membrane protein YaeT and three outer membrane lipoproteins. Genetic and biochemical evidence suggested that there might be additional members of this complex. Indeed, we discovered another component of the YaeT complex, the outer membrane lipoprotein small protein A (SmpA). Strains carrying loss-of-function mutations in smpA are viable but exhibit defects in outer membrane protein assembly. Biochemical experiments show that SmpA is involved in maintaining complex stability. Taken together, these experiments establish an important role for SmpA in both the structure and function of the YaeT complex.