This document describes the overall System Design of the SKA Observatory and its telescopes. It is a design perspective rather than a management, funding or organisational one. It serves to integrate all the system and sub-system designs to provide a coherent, authoritative description of the SKA1 Design Baseline. It also shows how the observatory, telescopes, and operations-design function together as an interconnected whole. In addition to summarising the entire design, it references primary sources of information as recorded in references interspersed throughout, which are mainly detailed documents drawn from the sub-system design work. It also describes the anticipated astronomical performance of the SKA and presents a framework for tracking performance from the design stage through construction to mature operations. It also describes the anticipated astronomical performance of the SKA and presents a framework for tracking performance from the design stage through construction to mature operations.