The concept of professional judgment is considered, including its theoretical foundations, how it is developed, and how it may be assessed. Professionals are asked to engage in complex and unpredictable tasks on society's behalf, and in doing so must exercise their discretion, making judgments--decide what is "best" in the particular situation rather than what is "right" in some absolute sense. Inevitably, some of these judgments lead to "error," which is endemic to professional practice. This challenges some current ideologies in health care regarding the primacy of evidence-based practice and the application of protocols. At the foundation of professional judgment is a form of knowledge--called practical wisdom--which is not formally taught and learnt but is acquired largely through experience and informal conversations with respected peers. Wisdom develops through "the critical reconstruction of practice," including deliberation, which is distinguished from mere reflection. Professionals need to engage in the appreciation of their practice--not just to understand what informs their own practice but to consider critically the contestable issues endemic to practicing as a professional.