Four years of war in Yemen have not only devastated the poorest country of the MENA region, but they have also generated new transnational layers of instability affecting the Arabian Peninsula and its neighbourhood. Threat level and perception at Saudi Arabia and Oman’s borders has decisively risen; Al-Qaeda in the Arabian Peninsula (AQAP) mostly targets Emirati-backed forces; migrants from Ethiopia and Somalia continue to reach Yemen despite the war; the conflict-saved Mahra region and the island of Soqotra are now stuck by inter-Gulf monarchies rivalries, which exported their rifts also to the Horn of Africa. (Re)discovering a peninsular perspective, this ISPI Dossier maps the security legacies of the conflict. How has Yemen turned into a regional spreader of instability? What about transnational insecurity? How has doing research and analysis on Yemen changed?