Polarization, Eh? explores the causes and consequences of the growing affective polarization and inter-partisan hostility in Canada. The cracks within Canadian society are now alarmingly clear, with Conservative party supporters becoming antagonistic towards Liberal and NDP voters and vice versa. This book explores the roots of these divisions while bringing us face-to-face with the consequences of our fragmenting political culture. An expert on public opinion and party politics, Eric Merkley argues that growing partisan hostility has emerged from a widening ideological divide between Conservatives on the right, and Liberal and NDP supporters on the left, which is a product of the polarization of Canada’s political parties over time. He provides evidence of this multi-step theory using cross-sectional and longitudinal survey data and multilevel modelling, while also ruling out several alternative explanations like online echo chambers and growing social group divides. The book employs survey data and embedded experiments to show how rising partisan hostility has heightened partisan-based motivations when Canadians navigate the social and political world, leading to biased reasoning, partisan discrimination, COVID-19 polarization, and support for anti-democratic behaviour by politicians. Polarization, Eh? highlights the dire need for institutional and societal reform to turn down the temperature in Canadian politics.