Amidst the many socio-ecological crises facing the world today, the biodiversity crisis is considered one of the most foundational. According to scientists, we have entered yet another mass extinction event in the history of the planet, though the first triggered by the impacts of the combined, uneven actions of one species. This introductory paper to a Special Section on the "Political ecologies of extinction" frames this crisis through political ecology, and explores what political ecologies of extinction could look like and focus on in the 21st century. Building on emerging literatures and the author contributions, it agrees that extinction is much more than the endpoint of a long and rocky road of the decline of a species. It is an uneven, historical process that conjoins political, geographical, socio-ecological, and other factors. Most of all, a political ecology of extinction highlights the intertwined forces of political economy, power and ecology whereby I argue that a special focus should be on how biological diversity and our understanding of it has changed over time, especially the last two centuries. The capitalist intensification of pressures on biological diversity combined with changing perceptions of the value of diversity during this time have led to a moment where extinction decisively moves from a biological endpoint to a political inflection-point. How to relate these two 'points' to historical and contemporary, local and global forces of political economy and power is central to political ecologies of extinction, as exemplified by the articles in this Special Section. This introductory article lays out their core themes, and derives from them further pointers and questions for developing this field.