The ITk Strip Tracker for the phase-II upgrade of the ATLAS detector of the HL-LHC

The current Inner Detector in the ATLAS experiment does not meet the requirements of the High Luminosity-LHC upgrade. A new detector, known as the Inner Tracker, will be built in place of the current Inner Detector and will consist exclusively of silicon based sensors. This contribution summarizes the on-going R&D activities within the different institutes involved in the phase II upgrade of the Strip Tracker. An update on the current status of testing and prototyping is given as well as the next steps before the submission of the ITk Strips Technical Design Report by the end of 2016.