For millennia, the smile has been recognised as a powerful communication device, offering benefits to both giver and receiver with few drawbacks. A sign of compassion, empathy and friendliness, smiling can benefit healthcare professionals and their patients, helping to build a relationship of trust. But beware the false smile, which is all too easily identified and may do more harm than good. In this review, we explore the literature surrounding smiling in healthcare and beyond, discussing the many reasons to be cheerful, from good health to a happy marriage, among aviators, table waiters, doctors, dentists and even dogs.