This study investigated the social networks developed by language learners during 14 weeks of an intensive English as a second language (ESL) program using the Study Abroad Social Interaction Questionnaire (Dewey, Bown, Baker, Martinsen, Gold, & Eggett, 2014; Dewey, Bown, & Eggett, 2012). It also utilized native speaker judgments to evaluate ESL fluency development. Results showed that participants were successful in developing complex social networks, that their oral fluency increased significantly, and that fluency gains were related to L2 social networks. Density (average number of people in a social group) was the most important predictor of fluency gain when only social network variables were considered. In a hierarchical regression, initial proficiency level and percentage of native English speakers in one’s network were the most significant of the established variables in the first step, and overall network size and density were the most important of the added social network variables in the second step.