This study aims to investigate whether English for Specific Purposes (ESP) reading relates to English as a foreign language (EFL) learners' identity and how they relate to each other if there is a link between the two. Via purposeful sampling, an experienced Taiwanese ESP reader in her 40s was recruited and received three life-story interviews. Borrowing Wenger's (1998) notion of social identity, the participant's ESP reading history is examined along (a) mutuality of engagement, (b) accountability to an enterprise, and (c) negotiability of a repertoire. The results show that ESP reading is tightly interwoven with the three dimensions. It is therefore determined that the two are related. Moreover, it is found they are highly interdependent and correlated as the participant's ESP reading proficiency varies with her positions in the communities of practice. Pedagogical implications relate to the need for teachers and ESP readers to raise their awareness of the learners' literate identities.