In 2009, a St. Louis glassblowing artist and recovering computer scientist named Jim McKelvey lost a sale because he couldn't accept American Express cards. Frustrated by the high costs and difficulty of accepting credit card payments, McKelvey joined his friend Jack Dorsey (the cofounder of Twitter) to launch Square, a startup that would enable small merchants to accept credit card payments on their mobile phones. McKelvey's fascinating and humorous stories of Square's early days are blended with historical examples of other world-changing companies built on the Innovation Stack to reveal a pattern of ground-breaking, competition-proof entrepreneurship that is rare but repeatable. The Innovation Stack is an irreverent first-person look inside the world of entrepreneurship, and a call to action for all of us to find the entrepreneur within ourselves and identify and fix unsolved problems⁠—one crazy idea at a time.