Why does your baby smile while asleep—and what can that tiny expression tell you? This warm, evidence-aware guide helps parents understand nocturnal grins without turning every twitch into a diagnosis. You will learn how early reflexive facial movements differ from the more socially responsive smiles that emerge as babies mature, how active sleep can bring changes in breathing, eyelids, mouths, and limbs, and why a sleeping smile does not reliably reveal a dream or a particular emotion. Clear explanations of infant sleep, feeding, comfort, and development help you observe patterns calmly and share useful details with a pediatrician or health visitor when needed. Practical checklists show what to note, when to let a sleeping baby rest, and which breathing, color, arousal, or illness signs deserve prompt medical advice. The book also respects babies who smile less, families whose cultures read expressions differently, and parents coping with anxiety, exhaustion, or postpartum low mood. Replace guesswork with informed observation and enjoy these fleeting moments without pressure to interpret them perfectly. Part of The Smile and Happiness Library.