This chapter examines adult thinking from the perspective of professional expertise and phronēsis, that is, practical wisdom. It first describes differences between experts and novices, and presents three conceptualisations of the development of expertise. This is followed by an analysis of the form of adult thinking referred to as integrative thinking, and phronēsis. The relationship of these two with expertise is examined. The analysis shows that professional expertise requires holistic thinking involving the ability to integrate or conciliate various and even conflicting perspectives in order to find new solutions to problems. Furthermore, the role of emotions and ethical reflection is emphasised. All this leads to the examination of practical wisdom, phronēsis, in particular. As a conclusion, a model of the nature of wisdom in professional expertise is presented, and it is suggested that the development of expertise and wisdom in the fast changing and complex world requires pedagogical approaches that support the integration and fusion of different forms of knowledge, various perspectives, and socially responsible ethical action and interaction in problem solving situations.