The 2016 election of Donald J. Trump invoked a time for reflection about the state of American politics and its deep ideological, cultural, racial, regional, and economic divisions. But one aspect that the contemporary discussions often miss is that these fissures have been opening over several decades and are deeply rooted in the structure of American politics and society. Nolan McCarty's Polarization: What Everyone Needs to Know® is an accessible introduction to polarization in America. McCarty takes readers through what scholars know and don't know about the origins, development, and implications of our rising political conflicts, delving into social, economic, and geographic determinants of polarization in the United States. While the current political climate makes it clear that extreme views are becoming more popular, McCarty also argues that, contrary to popular belief, the 2016 election was a natural outgrowth of 40 years of polarized politics, instead of a significant break with the past. He explains the factors that have created this state of affairs, including gerrymandered legislative districts, partisan primary nomination systems, and our private campaign finance system. He also considers the potential of major reforms such as instating proportional representation or single-transferable voting to remedy extreme polarization. A concise overview of a complex and crucial topic in US politics, this book is for anyone wanting to understand how to repair the cracks in our system.