Mathematicians have recently made dramatic progress on the Twin Primes Conjecture, which asserts that there are infinitely many pairs of prime numbers that differ by 2. This book will describe two stories: that of the recent work on the Twin Primes Conjecture, and in parallel the related ideas from the previous two thousand years of mathematics. Closing the Gap is among the clearest popular accounts of maths I've read in a while. It's about prime numbers, as the title suggests, but it's also a master piece in the art of weaving. Apart from exploring the mathematics, the book gives an intimate description of the process of doing maths as experienced by those who do it every day, and an account of a particularly exciting, and recent, period when prime number theory made some great leaps forward. And it's a look at a completely new way of doing mathematics: in large online collaborations that anyone can join.