It might seem as if globalization is making the whole world speak English. But spend time in any major city and you are likely to encounter a cornucopia of languages. Even monolingual people have different ways of speaking to their bosses or teachers, their intimate friends or their pets. And if you live in India or Nigeria, you might use five different languages during a typical day. Katrin Kohl makes a passionate case for why we must embrace languages in all their diversity. When you study a language, you open a unique doorway into the world, immerse yourself in a different way of seeing, and discover new ways of communicating with people from different cultures on their terms. Kohl argues that language diversity is of vital importance to human societies, sustaining the complexity of human nature, culture and technology. We should care about preserving it as much as we care about preserving the diversity of our biological world.