The envelope of Gram-negative bacteria consists of the periplasm and the murein cell wall bordered by the cytoplasmic and outer lipid bilayer membranes. Without specific machineries to export and secrete proteins into and across the cell envelope, bacteria would be unable to perform many essential functions. This co-ordinated collaborative project intends to make a major contribution to the structural and functional characterisation of complex membrane machineries involved in four distinct but related processes of protein or polymer translocation across the cell envelope of Gram-negative bacteria. The complete inventory of protein components of all of the systems is now available, providing a unique and essential framework for this project. We aim to understand how these machineries are organised, how they are assembled form individual subunits, how they are energised and how they function. The success of the project is guaranteed by the integration of the genetic, molecular, biochemical and structural expertise that individual members possess. The collective, active contribution of all members will create a unique, highly powerful consortium that will be the major world force in the study of the genesis and function of the bacterial cell envelope, with a ptentially major impact on biotechnology and pharmacy through the development of a greater understanding of fundamental processes specific to bacteria.