This Element describes the main theories that guide contemporary research in cognitive development along with research discoveries in several important cognitive abilities: attention, language, social cognition, memory, metacognition and executive function, and problem solving and reasoning. Biological and social contributions are considered side-by-side, and cultural contributions are highlighted. As children participate in social interactions and learn to use cultural symbols and tools to organize and support their thinking, the behaviors and understandings of the social community and the culture more broadly become an integral part of children's thoughts and actions. Culture, the natural ecological setting or habitat of human beings, plays a significant role by providing support and direction for cognitive development. Without the capacity to learn socially, human cognition would be markedly different from what it is today.