Dairy products generally require drying through a consistent application of relatively low heat. Drying is the process of thermally removing volatile substances (moisture) to yield a solid product. In today's rapidly changing scenario, application of optimization techniques is essential in food-processing industries to respond to the increasing demand for quality product in the market. Plenty of mathematical models were developed and used for understanding the process operations. However, the ultimate aim is either to minimize the effort required or to maximize the desired benefit. There has been a dramatic increase in the efficiency and reliability of optimization techniques. The first part of this chapter describes optimization tools such as response surface methodology, artificial neural network, finite element and finite volume numerical modelling. The latter part of this chapter focuses on the influence of process variables on the product quality of different drying process like drum drying, spray drying, freeze drying and spray freeze drying.