The ATLAS experiment is currently preparing for an upgrade of the inner tracking detector for High-Luminosity LHC operation, scheduled to start in 2026. The radiation damage at the maximum integrated luminosity of 4000 fb$^{-1}$ implies integrated hadron fluencies over 2x10$^{16}$ n$_{\textrm{eq}}$/cm$^2$ that require replacement of the existing Inner Detector. An all-silicon Inner Tracker (ITk) is proposed with a pixel detector surrounded by a strip detector. The current prototyping phase, targeting an ITk Strip Detector consisting of a four-layer central barrel and forward regions composed of six disks at each end, is described in the ATLAS Inner Tracker Strip Detector Technical Design Report (TDR). With the approval of the TDR by the CERN Research Board, the pre-production readiness phase has started at the institutes involved. In this contribution we present the design of the ITk Strip Detector, the current status of R&D on various detector components and preparations for production.