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.