The invention provides a cationic lipid comprising: (i) one head group, comprising one or more amino acids, in which at least one amino acid has a side chain that comprises a cationic moiety or a cationic precursor; (ii) a linking moiety of formula (5): —(HNR5)2NC(O)R3C(O)—  (5), wherein: each R5 is independently an optionally substituted C1-4 alkylene moiety; and R3 is an optionally substituted alkylene or alkenylene moiety; and (iii) two lipophilic moieties, wherein the head group and each of the lipophilic moieties are connected to the linking moiety through amide linkages.