Building on research on the development of reading and use of technology for language learning, this multiple-case study explored English as a second language (ESL) students' perceptions of using a social bookmarking Web 2.0 tool for the development of reading from an ecological perspective. Five students in a community college ESL course in the northeastern part of the USA participated in the study. The data sources included interviews, observations, e-journals, and artifacts. Thorough within-case and cross-case analysis of data revealed a number of Diigo affordances which ESL students found beneficial for their development of reading, the role of context and mode, participants' collaborative stance, and various aspects of influence Diigo had on ESL students' development of reading. The findings and discussion of the study highlight the role of social bookmarking tools in raising ESL students' motivation and engagement in reading. The study offers suggestions for further research and implications for practice.