The Sea of Marmara is a typical example of enclosed seas and an inland sea bounded by land-masses in four directions, and it links the Black Sea and the Mediterranean via the Bosphorus and the Dardanelles straits. Moreover, The sea of Marmara has strategic importance with possessing marine structures such as various types of terminals, cruise terminals, and marinas, and also providing a strong economic contribution with tourism revenue. This situation brings the necessity of determining the design wind and wave parameters properly. The wind and wave characteristics and their variabilities were evaluated covering the last 40 years (1979-2018) by using two well-known wind fields, i.e., ECMWF ERA-Interim and NCEP/CFSR. Wave parameters were generated from the calibrated and validated SWAN model with ERA-Interim wind data. The spatial and temporal variability of the long-term averages and long-term trends of the wind and wave characteristics were investigated, and also extreme wave conditions were evaluated in detail. This study shows that the modeling of waves in enclosed seas is more challenging compared to open seas due to several affecting factors such as land which affect the wave fields and need high spatial resolution. The results indicate that orography and islands largely affect the wind and wave climate in the Sea of Marmara. The northern side of the Sea of Marmara is characterized by stronger wind and wave climate compared to the southern side. The annual mean values of wave height have decreasing tendencies while the annual maxima tend to increase in most parts of the Sea of Marmara. The dominant wind and wave directions are observed to be in the northeast and southwest sector and their magnitudes are controlled by the orographic features over the Marmara Region.