This paper examines the geopolitics of insecurity in the Horn of Africa and the Arabian Peninsula. It focuses on the nexus of instability linking Somalia with Yemen and the states of the Gulf Cooperation Council (GCC) and contextualises it within a broader socio-political and economic crisis of governance in the region. It will adopt an interdisciplinary approach combining security studies with political science and international relations in a holistic study of the challenges of, and responses to, the incidence of progressive state failure in one of the most important geo-strategic and commercial world arteries. The security situation in Yemen became an issue of international concern following the attempted bombing of an American airliner in December 2009. Yet its roots extend much deeper, and form part of a complex security dilemma interlinking Yemen, and by extension the Arabian Peninsula, with state collapse in Somalia and instability in the Horn of Africa. Overlapping political, economic, social and environmental stresses in both countries has eroded state legitimacy and capacity, and bred extremism and myriad cross-border flows of militants, money and ideational affinity with trans-national terrorism. A reconstituted Al-Qaeda in the Arabian Peninsula now poses a renewed threat to regional and international security through its demonstrated intent and capability to operate in the GCC and beyond. The paper's primary aim is to explore the changing dynamics of regional security and chart GCC responses to these failing political economies on their flank. The GCC is the key regional stakeholder and has a collective interest in addressing the root causes of human insecurity and minimising their overspill to its own polities. Yet its record of engagement has hitherto been underwhelming, with a clear preference for a strategy of containment over serious consideration of the scale and complexity of the challenge posed by Yemen and Somalia. The paper will therefore assess the record of past and present GCC engagement with Yemen, in addition to the prospects for a constructive and sustained regional initiative in the future. Related to this is a secondary objective, which is the broadening of security to cover the emergence of increasingly non-military challenges to fragile polities in transition. Hence the paper will examine the intersection of resource depletion, unequal patterns of development and distribution, demographic and generational change, and the impact of climate change and environmental degradation in Yemen as a portent of longer-term challenges that will face the GCC.