If you haven't experienced Esther Perel's work yourself yet, you've probably heard someone you know talk about it — and likely express some very strong feelings. Perel is a psychotherapist and a bestselling author. Her 2006 book, Mating in Captivity, touched off a flurry of discussions and debates about eroticism and desire in long-term relationships. Her most recent book, The State of Affairs: Rethinking Infidelity is perhaps even more provocative. In it, she offers insights and advice about infidelity that challenge many of the assumptions of our culture. So what's all the fuss about? Here are a few of the key ideas that Perel promotes.