Concepts (i.e. lexicalised classes of real or fictitious entities) play a central role in many human intellectual activities, including planning, thinking, reasoning, problem solving, and decision making. How do people acquire concepts in the course of development and learning and use them in their thinking about the world? In this article, we attempt to provide an overview of conceptual development. We suggest that concepts can originate (1) in interactions with the world and get lexicalised later or (2) in the language and get grounded later. The first route is from category learning to a concept, and we discuss this route by focusing on the mechanisms of category learning and developmental changes in these mechanisms. The second route is from a word to a concept, and we discuss this route by focusing on inferring word meanings without visual referents. We then consider proposals of how concepts get organised into networks and hierarchies.