An exploration of the genesis of classical geopolitics lies in a conviction that location and resources are pivotal to the exercise of political power over territory. The term geopolitics was first coined in the late 1890s by the Swedish writer Rudolf Kjellén. Classical geopolitics, the term used to describe the earliest writings, was for Kjellén an intellectual field that recognised that it was “[a] science which conceives of the state as a geographical organism or as a phenomenon in space.” Later authors thought that geopolitics was more than a science. It was a way of understanding designed to signal a rather hard-nosed or realist approach to international politics. What made it reliable was its ability to generate law-like statements about the importance of the facts of physical geography, such as the distribution of landmass, the extent of the oceans, and the importance of particular, strategically located regions, in determining patterns of global political power. This article reviews in some detail the core features of this field—and interrogates a series of core ideas and principles at play. It also notes some other pertinent characteristics, such as the case that most classical geopolitical writers were committed nationalists and imperialists, under the intellectual influence of social Darwinism. The global map for these authors was fundamentally divided between the imperial great powers and the colonized world, now referred to as the Global South. Finally, these authors were convinced that they were offering a “god's eye view” of the world to fellow citizens and policy makers, uncorrupted by ideology or prejudice. The fate of classical geopolitics is uneven in the English-speaking world, in particular with a formal decline in the post-1945 period, signs of revival in the 1970s and 1980s, decline in the 1990s, and now re-emergence in a new era characterized by nationalism, nativism, populism. Animated concerns about borders and population composition and size provide fertile ground for old ideas to re-emerge about the needs of nation-states to secure their territories and peoples from others. The reader is introduced to a newer field critical geopolitics. It calls into question some of those core principles of classical geopolitics and emphasizes more the deliberate framing of space, the rejection of a hard separation between the domestic and the foreign, and it eschews the idea of the nation-state as a “living organism,” operating in a territorial container. It also draws attention to popular geopolitics, and the manner in which ideas about geography and cognate disciplines are produced and circulated through public cultures. Classical and critical geopolitics share a common concern—geography matters—but where they differ is how, where, and why geography matters.