The LII group study the fundamental principles for representing and reasoning about information in computer systems, based on symbolic logic, and their applications. A focus is on reasoning about change, e.g., using action logic, and in particular on the logical principles of information change. Central is formalisation of interaction in systems with several autonomous agents. Aspects of interaction which are interesting to formalise include the logical principles of trust, knowledge (epistemic logic) and rationality. Applications are found in social software, artificial intelligence, multi-agent systems and programming languages.