English for Specific Purposes (ESP) is an area of language education that has been advancing during the last years due to increased social and professional mobility. Despite this, as shown in the related literature, the area of ESP Teacher Education (TE) is deprived of attention by researchers; as a result, many ESP educators in different countries are General English (GE) teachers with insufficient training in ESP. The present chapter reports on the first findings of a technical action research study, which aims at exploring and addressing the problem of insufficient ESP TE among a specific group of ESP practitioners, suggesting an intervention in the form of an online ESP TE programme. Following the spiral pattern of action research, the study evolves in cycles of continuous improvement. This chapter focusses on the initial stages of the study during which the problem of lack of ESP TE opportunities was identified, and a remedy to this problem, an online ESP TE course, named Online Reflective Teacher Education in ESP (ReTEESP Online), was developed and piloted before its implementation. [For the complete volume, "ESP Teaching and Teacher Education: Current Theories and Practices," see ED595614.]