The words left and right often signal a political divide in debates about topics as diverse as abortion, capital punishment, gun control, social welfare, taxation, immigration, and the environment. Despite claims that political polarization is in decline, its persistence suggests that it is inherent to our society. At the same time, variations in the perception of each side indicate that these labels do not fully capture the reality of ideological disagreement. In Left and Right, Christopher Cochrane traces the origins of this political language to the very nature of ideology. What is ideology, what does it look like, and how does it manifest itself in patterns of political disagreement in Western democracies? Drawing on five decades of evidence from political scientists, including public opinion surveys, elite surveys, and content analysis of political party election platforms, Cochrane employs a new method to analyze the structure and evolution of the left/right divide in twenty-one Western countries since 1945. He then delves into the central argument of the book - that the language of left and right describes a meaningful, perceptible, and quantifiable pattern of political disagreement that has persisted over time and around the world. Calling for an adjustment to the way we view Canadian politics, Left and Right opens a window into the world of political ideologies - a world we see every day, but rarely analyze, define, or agree on.