Although basic facts about wealth inequality are no longer a mystery, we still know very little about who the wealthy are, how they got there, and what prevents other people from becoming rich. That is, we know very little about the process of wealth mobility. This book explores wealth by investigating some of the most basic questions about wealth mobility. How much mobility is there? Has the nature of mobility changed over time? Is entrepreneurship important? How much does inheritance matter? What other factors encourage or prevent wealth mobility, and how do these change over the course of a person's life?