This Business Plan shows how astronomers at the Armagh Observatory will deliver on the Observa- tory's key business areas in support of the Northern Ireland Executive's Programme for Government, the cross-cutting STEM Strategy and key actions and objectives of its sponsor government department, the Northern Ireland Department of Culture, Arts and Leisure (DCAL). First, we provide an introduction to the organization and the principal research themes in astronomy and related sciences addressed by sta in the Observatory and their international partners. The Observatory has a high-quality computing infrastructure, and a library, archives and astronomical museum collection that is one of the premier specialist collections of its kind.