This study draws on Sociocultural Theory to explore how 12 adult EFL learners engaged in pair work, how their willingness to engage was demonstrated in pair activities, and what other factors influenced that willingness. Six pairs engaged in seven different activities and were interviewed after all activities were completed. Each pair's type of interaction and each learner's perception of the interactions were analysed. Five distinct types of pair interactions were found from the pair work data, and most pairs showed more than two types of interactions when performing activities with the same partner. The interview data revealed that learners' willingness to engage with each other in pair work influences the nature of pair work and that willingness is influenced by the perceived difficulty of the activity and social considerations such as the partner's attitude and proficiency level. These findings suggest that what influences learner engagement is not the pair work per se but what learners bring to the pair work.