The review of current supervision models and instruments revealed a crucial need for a valid, reliable instrument that assesses the quality of the supervision environment as a venue for promoting counselor development. Therefore, the primary purpose of this study was the construction and initial validation of the Chae Optimal Supervision Environment Test (COSET). The five phases of scale development provided preliminary evidence of reliability and validity for the COSET. The COSET was administered to 93 counselor educators and clinical supervisors. Results indicated that the 15 item COSET possesses three factors: Emotional Environment, Learning Environment, and Power Environment. Reliability data also revealed that the COSET and its factors have adequate evidence of internal consistency. A three-factor COSET model demonstrated a good model fit using a confirmatory factor analysis. The results are largely supportive of the COSET as a scale to assess supervisors' creation of optimal supervision environments. Implications for the study and training of counselor supervisors were highlighted and suggestions for future research were reviewed. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]