Growth of aluminum films on clean Ta(110) surfaces has been investigated by LEED techniques. Five phases of aluminum have been found, which are: (1) disordered Al(111), formed by depositing atT<600°C; (2) Al(111)c(2×2) formed by heating film, deposited atT<300°C, to 700°C; (3) Al(100)c(2×2), formed by heating film, deposited 300<T<600°C, to 700°C; (4) Epitaxial Al(111), formed by depositing film with substrateTin range 600<T<670°C; (5) Diffuse phase, formed by heating any of the preceding to 800°C. Two orientations of each structure have been observed; this results from the close match between primitive unit meshes of aluminum (111), (100) and Ta(110). A mechanism for the growth of Al(111) and Al(100) is suggested. Comparisons with some published LEED data on epitaxy are made.