Motivation is thought to contribute to better text comprehension (Grabe, 2009), but L2 reading motivation of adult ESL students in the US is an underexplored area of research. The current study adopted self-determination theory—the concepts of intrinsic motivation, identified regulation, and controlled motivation, in particular—to examine IEP students’ motivation to read in English. The study also explored the relationship between the students’ L2 reading motivation and classroom instruction. The survey results of the study indicate that these students’ motivation to read was characterized more strongly by two relatively autonomous forms of motivation (i.e., intrinsic motivation and identified regulation). The content of the reading and engaging in peer discussions stood out as the classroom experiences that affected the students’ motivation to read in English. Pedagogical implications based on the study outcomes include providing the students with opportunities to compare their L1 and L2 reading experiences.