Infancy is the time of greatest change and fastest learning. The brain is still growing and at its most malleable. This is when the foundations of cognition are laid down. Starting from scratch, infants must learn to walk, talk, classify all the objects in their world and learn how to manipulate them. They must learn how to regulate their emotions and interact with other people. Infancy should therefore be of interest to researchers across all areas of psychology. But infants cannot answer question - naires or press buttons. Their attention span is even worse than undergraduates’. Infants are hard participants to find, to recruit and to schedule. They can be expensive and time consuming to test and only give small amounts of intrinsically noisy data. Research with infants presents considerable challenges and requires substantial ingenuity.