This subject introduces and discusses the foundational texts of the field. The aim of the subject is to equip students with an understanding of the theoretical underpinnings of particular developments in human–computer interaction, interaction design, and related areas so that they can extend the insights gained into the design and evaluation of new forms of technology as these continue to develop and are introduced into human activities. The subject includes readings from classic texts on different cognitive theories, influential in the development of human-centred design, such as behaviourism, cognitivism, situated action, and distributed, social and external cognition. These theories have influenced the various frameworks for representing users and their activities in user-centred design as well as the methods and tools that have shaped design practice in commercial environments. Major papers addressing these design methods and tools are also included.