a b s t r a c tThis paper represents a personal view of the state of HCI as a design discipline and as a scientific discipline, and how this is changing in the face of new technological and social situations. Going back 20 years a frequent topic of discussion was whether HCI was a 'discipline'. It is unclear whether this was ever a fruitful topic, but academic disciplines are effectively about academic communities and there is ample evidence of the long-term stability of the international HCI/CHI community. However, as in computer 'science', the central scientific core of HCI is perhaps still unclear; for example, a strength of HCI is the closeness between theory and practice, but the corresponding danger is that the two are often confused. The paper focuses particularly on the challenge of methodological thinking in HCI, especially as the technological and social context of HCI rapidly changes. This is set alongside two other challenges: the development of reliable knowledge in HCI and the clear understanding of interlinked human roles within the discipline. As a case study of the need for methodological thinking, the paper considers the use of single person studies in research and design. These are likely to be particularly valuable as we move from a small number of applications used by many people to a 'long tail' where large numbers of applications are used by small numbers of people. This change calls for different practical design strategies; focusing on the peak experience of a few rather than acceptable performance for many. Moving back to the broader picture, as we see more diversity both in terms of types of systems and kinds of concerns, this may also be an opportunity to reflect on what is core across these; potential fragmentation becoming a locus to understand more clearly what defines HCI, not just for the things we see now, but for the future that we cannot see.