At its core, political psychology is an inherently multidisciplinary field that aims to integrate insights from psychology, political science, sociology, and related disciplines to explain how people shape, and are shaped by, political phenomena across international borders. To these ends, the Cambridge Handbook of Political Psychology presents 41 chapters from world-renowned experts covering four distinct themes: (a) foundations of political psychology, (b) the politics of intergroup attitudes, (c) contemporary challenges to democracy, and (d) diversifying perspectives in political psychology. We thus showcase perspectives that are foundational to the field (e.g., rationale choice, ideology, individual differences, and public opinion), address enduring challenges to democracy (e.g., authoritarianism, racism, sexism, and immigration), and identify new threats that will shape the field for years to come (e.g., inequality, affective polarisation, political extremism, climate change, conspiracy theories, and populism). In doing so, we present the most comprehensive overview of political psychology to date that examines the origins of the field, where we are at today, and where we are headed for the future.