The mitochondrial proteome consists of more than 1000 proteins, yet only 13 of these are encoded by the mitochondrial genome. Thus, the vast majority of mitochondrial proteins is translated in the cytosol and imported into the organelle. This is carried out by dedicated import machineries that recognize client peptides, facilitate their translocation through the outer and the inner mitochondrial membrane and interact with downstream machineries to enable membrane insertion, protein folding and proteolytic processing. However, the molecular mechanisms underlying mitochondrial protein import remain poorly understood. We will combine cutting-edge structural biology with biophysical and biochemical methods to unravel the basic mechanisms underlying protein import in human mitochondria.