The paper reviews and discusses several definitions of wisdom. The aim is to stimulate and hopefully launch a debate regarding the challenges we face in our attempts to understand and harness it. The authors begin with reviewing the definitions of wisdom as kindness, well-being, and altruism, discuss practical wisdom in medicine and consulting, and introduce attempts to operationalise it as data compression. Further definitions consider the relation of wisdom to logic, intelligence, language, ageing, experience, insight, and faith. Following some theoretical considerations regarding uncertainty, heuristics, unconscious mind, and free will, the article concludes with an introduction to the concept of collective wisdom.