Russia and China make no secret of their enhanced cooperation, especially in light of their worsening ties with the US; the international sanction regime against Russia, the US' threatened withdrawal from the INF Treaty, and the US-China trade war, among other things, are driving Moscow and Beijing closer together. This dossier examines the security nexus of the Russia-China relationship. Specifically, it looks at both countries’ military transformation and security approach at the international level. If it is true that the global security environment is rapidly deteriorating and there is a "growing threat of nuclear war", as Vladimir Putin claimed in his annual end-of-year news conference, to what extent Russia's security alliance with China is seen as a threat by the liberal West? What military reforms are China and Russia implementing? How do their strategic cultures compare? Which are the main theatres where cooperation or competition between the two countries unfolds?