Siim is the CEO of Foundation CR14 since March 2022. CR14 is an Estonian cyber defence and security innovation centre, based on more than 11 years of military-grade cyber range experience in cybersecurity training, exercises, testing, experimentation and validation. Siim joined CR14 from the Estonian Information System Authority RIA where he was the founding Director of the European Union Cyber Capacity Building Network – or EU CyberNet. His other more recent appointments include being the Head of International Relations of the NATO CCDCOE, Deputy Director of Policy Planning at the Estonian MOD, and a diplomatic tour as Assistant Defence Counsellor at the Estonian Delegation to NATO. During the 2017 Estonian Presidency of the Council of the EU Siim acted as the Vice Chair of the Horizontal Working Party for Cyber Issues.