This paper illustrates how process data can be used to identify behavioral patterns in a computer-based problem-solving assessment. Using sequence-mining techniques, we identify patterns of behavior across multiple digital tasks from the sequences of actions undertaken by respondents. We then examine how respondents’ action sequences (which we label 'strategies') differ from optimal strategies. In our application, optimality is defined ex-ante as the sequence of actions that content experts involved in the development of the assessment tasks identified as most efficient to solve the task given the range of possible actions available to test-takers. Data on 7462 respondents from five countries (the United Kingdom, Ireland, Japan, the Netherlands, and the United States) participating in the Problem Solving in Technology-Rich Environment (PSTRE) assessment, administered as part of the OECD Programme for the International Assessment of Adult Competencies (PIAAC), indicate that valuable insights can be derived from the analysis of process data. Adults who follow optimal strategies are more likely to obtain high scores in the PSTRE assessment, while low performers consistently adopt strategies that are very distant from optimal ones. Very few high performers are able to solve the items in an efficient way, i.e. by minimizing the number of actions and by avoiding undertaking unnecessary or redundant actions. Women and adults above the age of 40 are more likely to adopt sub-optimal problem-solving strategies.