The present invention provides targeting lipids of structure (Cl) L100 -linker - L101 where L100 is a lipid, lipophile,alkyl, alkenyl or alkynyl, L101 is a ligand or - CH2CH2(OCH2CH2)p O(CH2)q CH2-ligand, p is 1-1000, and q is 1-20. In addition, theinvention provides compositions and methods for the delivery of therapeuticagents to cells. In particular, these include novel lipidsand nucleic acid-lipid particles that provide efficient encapsulation ofnucleic acids and efficient delivery of the encapsulated nucleicaicd to cellsin vivo.