This document discusses the issue of who is qualified to teach English for Specific Purposes (ESP) classes: a content specialist or a language teacher. It notes that while content specialists have strong subject knowledge, they may lack language teaching skills, and language teachers may lack deep subject matter expertise. The document recommends that ESP teachers have a positive attitude towards the content, a basic knowledge of subject principles, and awareness of students' existing knowledge. Additionally, ESP teachers should focus on meeting students' language needs through the subject matter, rather than becoming subject matter experts themselves.