The study of factors influencing undergraduate learners’ participation and/or reticence in second/foreign language classrooms, a relatively recent line of research, can contribute to the betterment of language teaching and learning practices. In this work, we attempt to investigate the causes of a population of undergraduate English as a foreign language (EFL) learners’ reticence by focusing on their own perceptions and by seeing the problem from their perspective. 201 male and female undergraduate Iranian EFL learners selected randomly based on Krejcie and Morgan’s formula for determining sample size served as the participants of the study. The data were collected through interviews, observations and a five-point Likert-scale researcher-made questionnaire. The results of the analyses of the data through qualitative content-based coding of the transcripts, frequency counts, and factorial analysis of the questionnaire responses revealed the following: a) based on systematic class observations, most students appeared to understand teachers’ instruction, took notes, and spoke when addressed; however, they rarely asked questions or volunteered responses; b) unfriendly and competitive class atmosphere, boring and useless topics and materials, and having unmotivated and serious teachers were among the most  frequent  learner-perceived factors causing reticence; c) based on the results of exploratory factorial analysis, 12 factors including  learner anxiety,  poor class management, peer/ teacher correction,  background knowledge, grouping learners, and self-image were reported as the main causes of reticence. Based on these findings, we make suggestions for EFL teachers about how to consider students’ concerns and to promote class participation.