A cationic lipid of Formula A: wherein: R 1 and R 2 are independently selected from H, (C 1 -C 6)alkyl, heterocyclyl, and polyamine, wherein said alkyl, heterocyclyl and polyamine are optionally substituted with one to three substituents selected from R'; or R 1 and R 2 can be taken together with the nitrogen to which they are attached to form a monocyclic heterocycle with 4-7 members optionally containing, in addition to the nitrogen, one or two additional heteroatoms selected from N, O and S, said monocyclic heterocycle is optionally substituted with one to three substituents selected from R'; R 3 is independently selected from (C 4 -C 20)alkyl and (C 4 -C 20)alkenyl, said alkyl or alkenyl optionally substituted with one to three substituents selected from R'; R 4 is independently selected from (C 1 -C 16)alkyl and (C 1 -C 16)alkenyl, said alkyl or alkenyl optionally substituted with one to three substituents selected from R'; R 5 is independently selected from (C 4 -C 8)alkyl or (C 4 -C 8)alkenyl, said alkyl or alkenyl optionally substituted with one to three substituents selected from R'; R 6 is (C 1 -C 2)alkyl, said alkyl optionally substituted with one to three substituents selected from R'; Q 1 and Q 2 are each, independently, a bond, -OC -, -C O-, -SC -, -C S-, -OC -, - S-S-, -C(R")=N-, -N=C(R")-, -C(R")=N-O-, -O-N=C(R")-, -C (NR")-, -N(R")C -, C (NR")-, -N(R")C -, -N(R")C N(R")-, -OC O-, OSi(R") 2 O-, -C (CR" 2)C O-, or -OC (CR" 2)C -, with the proviso that when either Q 1 or Q 2 is a bond then the other is not a bond; each occurrence of R' is independently selected from halogen, R", OR", SR", CN, CO 2 R" or CON(R") 2; R" is independently selected from H and (C 1 -C 6)alkyl, wherein said alkyl is optionally substituted with halogen and OH; n is 0, 1, 2, 3, 4 or 5; or a pharmaceutically acceptable salt or stereoisomer thereof. R 1 and R 2 are independently selected from H, (C 1 -C 6)alkyl, heterocyclyl, and polyamine, wherein said alkyl, heterocyclyl and polyamine are optionally substituted with one to three substituents selected from R'; or R 1 and R 2 can be taken together with the nitrogen to which they are attached to form a monocyclic heterocycle with 4-7 members optionally containing, in addition to the nitrogen, one or two additional heteroatoms selected from N, O and S, said monocyclic heterocycle is optionally substituted with one to three substituents selected from R'; R 3 is independently selected from (C 4 -C 20)alkyl and (C 4 -C 20)alkenyl, said alkyl or alkenyl optionally substituted with one to three substituents selected from R'; R 4 is independently selected from (C 1 -C 16)alkyl and (C 1 -C 16)alkenyl, said alkyl or alkenyl optionally substituted with one to three substituents selected from R'; R 5 is independently selected from (C 4 -C 8)alkyl or (C 4 -C 8)alkenyl, said alkyl or alkenyl optionally substituted with one to three substituents selected from R'; R 6 is (C 1 -C 2)alkyl, said alkyl optionally substituted with one to three substituents selected from R'; Q 1 and Q 2 are each, independently, a bond, -OC -, -C O-, -SC -, -C S-, -OC -, - S-S-, -C(R")=N-, -N=C(R")-, -C(R")=N-O-, -O-N=C(R")-, -C (NR")-, -N(R")C -, C (NR")-, -N(R")C -, -N(R")C N(R")-, -OC O-, OSi(R") 2 O-, -C (CR" 2)C O-, or -OC (CR" 2)C -, with the proviso that when either Q 1 or Q 2 is a bond then the other is not a bond; each occurrence of R' is independently selected from halogen, R", OR", SR", CN, CO 2 R" or CON(R") 2; R" is independently selected from H and (C 1 -C 6)alkyl, wherein said alkyl is optionally substituted with halogen and OH; n is 0, 1, 2, 3, 4 or 5; or a pharmaceutically acceptable salt or stereoisomer thereof.