The ATLAS experiment is currently preparing for an upgrade of the tracking system in the course of the High-Luminosity LHC that is scheduled for 2026. The radiation damage at the expected integrated luminosity of $4000\;\mathrm{fb}^{-1}$ and hadron fluencies over $2\times10^{16}\;\mathrm{n}_{\mathrm{eq}}/\mathrm{cm}^{2}$ requires a replacement of existing Inner Detector by an all-silicon Inner Tracker with a pixel detector surrounded by a strip detector. The ATLAS ITk detector will enable to bring Level-0 trigger rate of a few MHz down to a Level-1 trigger rate below 1 MHz at the peak instantaneous luminosity of $7.5\times10^{34}\;\mathrm{cm}^{-2}\mathrm{s}^{-1}$ that corresponds to approximately 200 inelastic proton-proton interactions per beam crossing. The current prototyping phase, that is working with ITk Strip Detector consisting of a four-layer barrel and a forward region composed of six disks on each side of the barrel, has resulted in the ATLAS Inner Tracker Strip Detector Technical Design Report, which starts the pre-production readiness phase at the involved institutes. In this contribution we present the design of the ITk Strip Detector and current status of R&D of various detector components.