The OECD Programme for the International Assessment of Adult Competencies (PIAAC) was the first computer-based large-scale assessment to provide anonymised log file data from the cognitive assessment together with extensive online documentation and a data analysis support tool. The goal of the chapter is to familiarise researchers with how to access, understand, and analyse PIAAC log file data for their research purposes. After providing some conceptual background on the multiple uses of log file data and how to infer states of information processing from log file data, previous research using PIAAC log file data is reviewed. Then, the accessibility, structure, and documentation of the PIAAC log file data are described in detail, as well as how to use the PIAAC LogDataAnalyzer to extract predefined process indicators and how to create new process indicators based on the raw log data export. The Programme for the International Assessment of Adult Competencies (PIAAC) is an Organisation for Economic Cooperation and Development (OECD) study that assesses and analyses adult skills in the cognitive domains of literacy, numeracy, and problem solving in technology-rich environments (PS-TRE). The computerbased assessment requires respondents to solve a series of tasks (items). The tasks are related to information presented to the respondent on the screen (e.g. a text from a newspaper, a simulated webpage). When solving a task, the respondent interacts with the assessment system-for example, by entering or highlighting text or clicking graphical elements, buttons, or links. The assessment system logs all these interactions and stores related events (e.g. keypress) and time stamps in log files.