This study examines the longitudinal trajectories of two Korean ESL immigrants' L2 learning motivation from an Activity Theory perspective. Two highly skilled immigrants participated in monthly semistructured interviews over a period of 10 months. The research questions are as follows: (1) How does the relationship between ESL learners and their perceived social contexts affect and shape the way in which their ESL learning motivation develops? (2) How can the factors affecting the changes in ESL learning motivation be explained from an Activity Theory perspective? The recurring themes in the monthly interview data were coded and aligned to Engestrom's (1999a) activity-system model; important interactions among the subcomponents of the model are presented and discussed. The results indicate that (1) the dynamism in ESL learning (de)motivation can be coherently explained in a series of longitudinal activity-system models; and (2) that it is not the ESL context per se but each participant's recognition of it that plays a pivotal role in creating, maintaining, and terminating ESL learning motivation. (Contains 8 figures, 1 table, and 3 notes.)