How much knowledge is necessary for action? This question is fundamental because it suggests that the link between knowledge and action is debatable, that there is no given, fixed causal relationship between knowledge and action. In addition, there seems to be no fixed causal direction. Knowledge can be a prerequisite for action but also a consequence of an action. My opening question relates two key words in psychology. One of them is knowledge, about which a large body of knowledge exists (e.g., Halford, Wilson, & Phillips, 2010)-about its different types (e.g., procedural, declarative), styles of acquisition (implicit, explicit), and degrees of accessibility (conscious, subconscious, unconscious). The other word is action, about which there are various theories describing human behavior with respect to intention (e.g., Fishbein & Ajzen, 2010). In this introductory section I try to give an overview of these conceptions and of the relation between knowledge and action.The issues around the keywords knowledge and action-which constitute the title of a book by Frey, Mandl, and von Rosenstiel (2006)-are captured by the following four main aspects, which generate corresponding questions.1. The relation between knowledge and action. From the perspective of the psychology of knowledge (e.g., Strube & Wender, 1993), knowledge is a competence for action, a precondition. What is known about the relation between knowledge and action and what is not known? How much of human action is governed by routines, experience, intuition, and knowledge? What is the tradeoff between taking action and improving knowledge? 2. Types of knowledge and different phases. To what extent do various types of knowledge (e.g., implicit or explicit) influence the steps from cognition to action (e.g., aspirations, attention, decision-making, problem-solving, the evaluation of situations, the search for alternatives, and the implementation of intentions)?