The paper presents the research design used for identifying and validating a set of competencies required of ESP (English for Specific Purposes) teachers. The identification of the competencies and the three-stage validation process are also discussed. The observation of classes of ESP teachers for field-testing the validated competencies and evolving of the competency scale for ESP teachers are also presented. The research design and the methodology followed are given hoping that this will serve as a model for future research on teacher competency.