The current ATLAS Inner Detector will be upgraded to the Inner Tracker detector for its operation at the High Luminosity Large Hadron Collider. The Inner Tracker will be an all-silicon detector divided into two sub-detectors: four layers of strip sensors will form the strip detector, and five barrel and a number of endcap layers of pixel sensors will form the pixel detector. Local support structures will mechanically support the silicon modules and some of the services including cooling pipes. Specialised carbon-based structures have been designed to optimise performance and provide hermetic coverage. The design of these structures, as well as their thermal, mechanical, and electrical properties, have been qualified by direct tests on prototypes. In this document, the novel designs, assembly procedures, and qualification techniques used to prove their adherence to specifications will be discussed together with the obtained results. Finally, plans for production, expected to start in mid 2023, will also be introduced.