© Coastal Education and Research Foundation, Inc. 2020.Balas, L.; Genc, A.N., and Eser, E., 2020. Transitional waters typology in Turkey: Melen Estuary case study. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 18-22. Coconut Creek (Florida), ISSN 0749-0208. Transitional and coastal water bodies are dynamic and complex environments. Even though widespread typological descriptors have been defined for coastal waters, typology studies for transitional waters are still continuing in Turkey as in many European countries. Transitional waters include estuaries, lagoons, and deltas. In this manuscript, the typology study applied for the Melen estuary is presented. Melen Estuary located in the Western Black Sea Part of Turkey is one of the significant watersheds of Turkey as it supplies more than 50% of the drinking water to the city of Istanbul. In typology approach, System B is accepted, and the Guidance Document No 5 produced by the Common Implementation Strategy for the Water Framework Directive (2000/60/EC) Working Group 2.4 (COAST) is closely followed. In addition to the obligatory factors, current velocity, wave exposure, and mixing characteristics are investigated as the optional factors. Measurements and modeling studies are used together. The coastal processes in the Melen Estuary are modelled. The wind and wave climate, wind and wave-induced current patterns, and mixing zone are simulated by HYDROTAM-3D (Three dimensional hydrodynamic, transport and water quality model). In the long term directional wind analyses, six hourly predictions of the European Centre for Medium-Range Weather Forecasts (ECMWF) between 2000-2019 are analyzed. In the long term directional wave statistical analysis, six hourly wave predictions of ECMWF between 2000-2019 operational archive are used. The range of significant wave heights, with 12 hours/year exceedance probability, is estimated as 0.4m≤Hs,12≤3.2 m. The wave exposure index for Melen transitional water is calculated. The dominant wave direction interval is determined as North-Northeast. Based on the mixing studies, the degree of stratification is determined as partially stratified.