This chapter discusses the information about bacterial transport systems with special attention to ''active'' transport processes coupled to electron transfer systems. Accumulation of solutes in right-side-out membrane vesicles is only observed in the presence of electron donors. Electron carriers can use the redox energy for the translocation of protons across the cytoplasmic membrane, normally from the inner to the outer aqueous compartment. Membrane-permeable ions will distribute across the membrane according to the membrane potential. Weak acids or bases which are membrane permeable in neutral form will distribute across the membrane according to the pH gradient. The electron carriers are tightly incorporated in the membrane, and functional respiratory chains are found in membrane vesicles isolated from many bacteria. Insight into the mechanism of solute transport through the cell envelope requires knowledge about the mechanism of solute translocation across the cytoplasmic membrane and the coupling of this process to the cell’s energy generating machinery.