Teacher professional development as a significant aspect of any educational context due to its complex and dynamic nature has been perceived, designed, and delivered differently by various professionals. A more traditionally oriented perspective regards it as a one-shot practice at initial teacher education programs, while the more dynamic view emphasizes its continuity and sustained nature developing during one's profession. Despite the recent growth of interest in the latter, studies investigating the issue through teachers’ lens as critical agents in their professional development in Iran are underdeveloped. The present qualitative study explores a group of Iranian experienced English language teachers' perspectives in this regard in two contexts of high schools and language institutes. Semi-structured interviews were conducted to collect experienced teachers’ views regarding professional development. The body of transcribed data explored through open, focused, and axial coding procedures led to three significant themes, namely the teachers' understanding of professional development, their beliefs about the authority/institute/organization/ responsible for teacher professional development, and their suggestions for improving the status quo of professional development, each theme including specific subthemes. The result of the interviews underscored the need for a combination of theory, practice, and teacher as the three fundamental sides of a triangle, indicating that teacher education courses should be guided by teachers as a principal-agent along with teacher trainers and educators to have a voice to share their valuable personal practical knowledge and experience. The emic understanding gained through this study has implications for teacher education curriculum developers, administrators, supervisors, and TTC trainers.