Turkey is the largest hazelnut producer in the world, and has a surplus of about 100,000 ton per year. Current knowledge about the properties of Turkish hazelnut, microbiological and chemical changes during postharvest treatments and processing are reviewed. Microbial activities bring about significant quality loss due to inadequate harvest, drying, and storage methods and conditions. Storage, shelling, roasting, and packaging conditions and methods may contribute to lipid oxidation and subsequent rancidity that reduces shelf life of the hazelnut and its products. Roasting methods and conditions determine the color and aroma formed. Improvement of harvest, post-harvest, and processing conditions and methods should improve quality, but the best quality can only be attained if the whole production and processing line is designed and operated properly.