What is imperialism? For Marxists, starting with Lenin and Bukharin, imperialism represents a necessary stage in the development of world capitalism, which consists of not simply competition between firms, but between states over world domination. As Bukharin wrote, when capitalist production bursts the boundaries of the national state, there inevitably develops “a conflict, which…is settled through extending the state frontiers in bloody struggles, a settlement which holds the prospect of new and more grandiose conflicts.” This talk will discuss the debates that shaped the development of a Marxist theory of imperialism, and assess their ongoing relevance to our situation today.