The Cherenkov Telescope Array Observatory (CTAO) will be the first ground-based gamma-ray observatory and the world’s largest instrument for gamma-ray astronomy. It will detect high-energy radiation from the Universe with unprecedented accuracy and better sensitivity than any current instrument, providing novel insights into the most extreme events in the Universe. The CTAO gGmbH is the interim legal entity in the preparation of the design and implementation of the CTAO, until the final legal entity, a European Research Infrastructure Consortium (CTAO ERIC), is achieved. The CTAO ERIC will be responsible for the construction and operation of the Observatory. CTAO has four locations: the Headquarters currently in Heidelberg (Germany) moving to Bologna (Italy), the Science Data Management Centre (SDMC) in Zeuthen (Germany), and the two telescope array sites at the two hemispheres. CTAO’s Northern Array Site is located on the existing site of the Instituto de Astrofísica de Canarias’ (IAC’s) Observatorio del Roque de los Muchachos on the island of La Palma (Spain). CTAO’s Southern Array Site is less than 10 km southeast of the European Southern Observatory’s (ESO’s) existing Paranal Observatory in the Atacama Desert (Chile). Three classes of telescopes spread over a large area will be installed: Large-Sized Telescopes (LST, 23m diameter), Medium-Sized Telescopes (MST, 12m diameter), and Small-Sized Telescopes (SST, 4m diameter). More than 1,500 scientists and engineers from 25 countries and approximately 150 research institutes participate in the CTA Project, working in close cooperation with the CTAO for the definition of the instrument design and the scientific programme. CTAO was added as an emerging project to the 2006 ESFRI Roadmap of European research infrastructures and as a regular project in the 2008 edition, making it part of the European strategy to guarantee European Scientists access to first-rate infrastructures.