What is a must-read book? For me, it’s a book that explores, in a compelling way, a must-know idea — one that altered my perspective long after I had forgotten the book’s narrative and details. The following five books are a small sample from a longer list of must-reads, but they have two things in common. First, they forced me to confront how superficial and inadequate my thinking was in assessing different kinds of complex problems. Second, they took the important next step of introducing more sophisticated approaches to tackling complexity, which I have been using ever since.