We are not alone. We are home to a trillion cells that are not our own, but are very much the making of us. Both on us and inside us live bacteria, viruses, protozoans, fungi, worms, lice and mites that we carry throughout our lives. Our private wildlife keeps us healthy, sometimes makes us ill and even changes our behaviour. Only now are we beginning to understand the full story behind our microbial tenants and what they can teach us about ourselves. We are not simply human, we are a unique and diverse collection of life forms. This is the untold story of Life on us.