Recent research has expanded understanding of the contribution of emotions to student engagement and achievement. Achievement emotions can be conceptualized as general ways of responding to achievement settings or specific emotional states aroused during a specific learning activity. Emotion processes can be distinguished as positive or negative, activating or deactivating. Using data from an international survey of science achievement (PISA 2006; N > 400,000 15-year-old students from 57 countries), relations between the positive, activating achievement emotion of enjoyment and a number of variables that combine with enjoyment to define students’ engagement with learning science are examined. Previously, we reported that enjoyment is central to relations between interest in science, value and knowledge, and students’ reported current and future engagement. The embedded attitudinal items from PISA 2006 allow testing of how enjoyment contributes to a more direct measure of engagement with science by assessing students’ interest in finding out more about the specific topics used to measure their science achievement. In this investigation, structural equation modeling is used to test predictions based on Hidi and Renninger’s (2006) four-phase model of interest development, and Pekrun’s (2006) control-value theory of achievement emotions.