A non-phthalate catalyst system for olefin polymerization, comprising: (a) a solid Ziegler-Natta catalyst composition comprising a transition metal, a Group 2 metal, and one or more halogens; and one or more internal electron donor compounds having the structure of a cyclic diester compound having a formula of wherein: each R 9 is independently H, halogen, or a C 1 to C 18 hydrocarbyl group, each R 10 is independently a C 1 to C 20 hydrocarbyl group; each of R 11 and R 12 is independently R 9 or -COOR 10, provided that at least one of R 11 and R 12 is -COOR 10; p is an integer from 1 to 6; and wherein each R 9 can contain one or more heteroatoms that replace one or more carbon atoms in the hydrocarbyl group, wherein the one or more heteroatoms are selected from the group consisting of halogens, P, N, O, S, and Si; and (b) one or more external electron donor compounds selected from the group consisting of: i) a triester compound having a formula of ii) a diester compound having a formula of and iii) an oxo-substituted diester compound having a formula of wherein: X is CH 2 or O, each R is independently a C 1 -C 10 hydrocarbyl group, each R' is independently H or R, each n is independently an integer from 1 to 4, and n' is an integer from 0 to 4. (a) a solid Ziegler-Natta catalyst composition comprising a transition metal, a Group 2 metal, and one or more halogens; and one or more internal electron donor compounds having the structure of a cyclic diester compound having a formula of wherein: each R 9 is independently H, halogen, or a C 1 to C 18 hydrocarbyl group, each R 10 is independently a C 1 to C 20 hydrocarbyl group; each of R 11 and R 12 is independently R 9 or -COOR 10, provided that at least one of R 11 and R 12 is -COOR 10; p is an integer from 1 to 6; and wherein each R 9 can contain one or more heteroatoms that replace one or more carbon atoms in the hydrocarbyl group, wherein the one or more heteroatoms are selected from the group consisting of halogens, P, N, O, S, and Si; and each R 9 is independently H, halogen, or a C 1 to C 18 hydrocarbyl group, each R 10 is independently a C 1 to C 20 hydrocarbyl group; each of R 11 and R 12 is independently R 9 or -COOR 10, provided that at least one of R 11 and R 12 is -COOR 10; p is an integer from 1 to 6; and wherein each R 9 can contain one or more heteroatoms that replace one or more carbon atoms in the hydrocarbyl group, wherein the one or more heteroatoms are selected from the group consisting of halogens, P, N, O, S, and Si; and (b) one or more external electron donor compounds selected from the group consisting of: i) a triester compound having a formula of ii) a diester compound having a formula of and iii) an oxo-substituted diester compound having a formula of wherein: X is CH 2 or O, each R is independently a C 1 -C 10 hydrocarbyl group, each R' is independently H or R, each n is independently an integer from 1 to 4, and n' is an integer from 0 to 4. i) a triester compound having a formula of ii) a diester compound having a formula of and iii) an oxo-substituted diester compound having a formula of X is CH 2 or O, each R is independently a C 1 -C 10 hydrocarbyl group, each R' is independently H or R, each n is independently an integer from 1 to 4, and n' is an integer from 0 to 4.