Schematic showing phospholipid transport from the endoplasmic reticulum (ER) to all bilayer leaflets of the mitochondrial double membrane. Non-vesicular mechanisms deliver ER-synthesized phospholipids to the cytoplasmic face of the outer mitochondrial membrane (OMM). The lipids are scrambled across the OMM by a lipid transporter (scramblase) before moving through the intermembrane space (IMS) and across the inner mitochondrial membrane (IMM).