Abstract : This document introduces current concepts and techniques relevant to the design and implementation of user interfaces. A user interface refers to those aspects of a system that the user refers to, perceives, knows and understands. A user interface is implemented by code that mediates between a user and a system. This document covers both aspects. The first chapter is an introduction to the psychology of human-computer interaction. It presents the theoretical models that have had a significant impact on the evolution of the field. These models offer a way to organize the design process and help understand the cognitive process involved in interacting with a computer. The rest of the document is concerned with the software design of user interfaces and shows how the principles established by the cognitive principles can be put into practice. Following a presentation on the abstractions involved in the organization of an interactive system, attention is then directed to the tools for constructing user interfaces: windowing systems, tool kits and user interface management systems.