Interaction analyses comes out of (micro)sociology and is the study of how humans interact with each other in their environment in real time. One of the core insights of interaction analysis is the notion of 'recipient design’: any contribution to interaction - be it a turn at talk, nonverbal behaviour or a combination of both - will always be formulated for a specific recipient. Not only do we adjust our contributions according to what we perceive as the other participants' understanding, but we also adjust our actions according to other participants' knowledge and understanding format our actions in their very details for the knowledge and understanding of specific other participants.
The other core insight is that the meaning of what is said or done is neither in the action itself, nor in the spoken word but in the way it is received, that is in the way the other participants respond to a previous action. For example, I can show that I understand the phrase ‘what’s up' as a greeting by greeting back. Or maybe more complex: stories are typically received by other stories, which means that through the story I tell following yours I show you how I understood the story you told me. So interaction analysis does not operate with meaning as something that is in the head of the speakers or in the words but in what the participants show as joint understanding. Interaction analysis is interested in shared meaning, in inter-subjectivity.
Interaction analysis has developed tools, methods and techniques to describe emerging interaction in great detail and is able to provide interaction designers with the most detailed and delicate ways to understand user activities.