A peptide having an amino acid sequence containing at least eight consecutive amino acids of the human lactoferrin protein or of the bovine lactoferrin protein. The peptide is suitable as a cell-penetrating peptide. A complex of the peptide and a cargo molecule non-covalently bound to the peptide. The cargo molecule may be a nucleic acid, an amino acid, a peptide, a protein, a carbohydrate, a lipid, or a small molecule. A method of penetrating or transfecting a cell using the complex.