In Escherichia coli, lipopolysaccharide (LPS) is synthesized at the inner membrane and transported to the outer membrane for assembly. This is known to be mediated by LPS transport (Lpt) proteins: LptBFG forms a complex with the inner-membrane-bound LptC, which binds to LptA, and LptA interacts with LptD at the outer membrane, forming a trans-envelope bridge that connects the two membranes. Here, the authors elucidate the individual steps of LPS transport across the Lpt bridge. They found that LPS is extracted from the inner membrane by LptBFG, which then transports it to LptC; LPS is then transferred to LptA. Importantly, both transport events required ATP, so the authors propose that multiple rounds of ATP hydrolysis provide energy to push LPS from the inner to the outer membrane through the trans-envelope bridge.