It is sometimes said that a theory only lasts until the next one comes along. Although there are times this is true, elements of previous theories often survive alongside newer thinking, at least until ‘the theory of everything’ exists as something other than a film about the physicist, Stephen Hawking. This chapter talks about some of those who have influenced current thinking about how children mature, particularly in terms of their social and emotional development. Vygotsky may be best known for what he called, ‘the zone of optimal development’. This he described as the gap between what children could discover on their own and their level of potential development under adult guidance or in collaboration with more capable peers: Vygotsky used the term ‘scaffolding’ which is still in use today. Maslow was one of the founders of humanistic psychology, which tries to help people fulfil their potential and maximise their wellbeing rather than concentrating on dysfunction.