The article discusses the challenges posed by ubiquitous computing to human-computer interaction (HCI) and interaction design. Traditional HCI has focused on single users interacting with computers through screens, keyboards, and mice. However, ubiquitous computing introduces the concept of context-aware computing, where systems can sense and respond to their environments. The term "context" is central to this area but is often misunderstood. The paper argues that conventional interpretations of context misrepresent its role in everyday human activity and proposes an alternative model for design. The paper explores two major research issues in ubiquitous computing: the relationship between physical form and activity, and how computation can be made sensitive to its setting. The first issue involves designing computationally-enhanced devices that interact with the physical world. The second focuses on making systems responsive to their environments through sensor technologies. Context is used in two ways in ubiquitous computing systems: as a retrieval cue or to dynamically tailor system behavior. Examples include systems like Lifestreams and Easy Living. The paper also discusses the social aspects of context, emphasizing the need for systems to be sensitive to social settings. Social scientists argue that traditional system design often fails to respond to the setting in which action occurs. By incorporating context, system designers aim to make their systems more responsive to different social settings. The paper highlights the challenges of translating social and technical ideas into design. While ubiquitous computing systems may be more responsive, they often fail to address sociological critiques. The goal of the paper is to explore the relationship between technical and social aspects of context and to examine the mismatch between them. It concludes by asking, what do we talk about when we talk about context?The article discusses the challenges posed by ubiquitous computing to human-computer interaction (HCI) and interaction design. Traditional HCI has focused on single users interacting with computers through screens, keyboards, and mice. However, ubiquitous computing introduces the concept of context-aware computing, where systems can sense and respond to their environments. The term "context" is central to this area but is often misunderstood. The paper argues that conventional interpretations of context misrepresent its role in everyday human activity and proposes an alternative model for design. The paper explores two major research issues in ubiquitous computing: the relationship between physical form and activity, and how computation can be made sensitive to its setting. The first issue involves designing computationally-enhanced devices that interact with the physical world. The second focuses on making systems responsive to their environments through sensor technologies. Context is used in two ways in ubiquitous computing systems: as a retrieval cue or to dynamically tailor system behavior. Examples include systems like Lifestreams and Easy Living. The paper also discusses the social aspects of context, emphasizing the need for systems to be sensitive to social settings. Social scientists argue that traditional system design often fails to respond to the setting in which action occurs. By incorporating context, system designers aim to make their systems more responsive to different social settings. The paper highlights the challenges of translating social and technical ideas into design. While ubiquitous computing systems may be more responsive, they often fail to address sociological critiques. The goal of the paper is to explore the relationship between technical and social aspects of context and to examine the mismatch between them. It concludes by asking, what do we talk about when we talk about context?