Appropriate for students with no previous experience of operator theory, the three-part approach covers linear algebra and finite dimensional systems, operators in Hilbert space, and linear systems in Hilbert space. The treatment's most significant feature lies in its focus on the centrality of module structure in several settings. Linear algebra, structure of self-adjoint and unitary transformation, and the structure of restricted shift operators are developed in similar ways, with emphasis on the connections between their theorems. Each section concludes with notes and references.