A great many of the mathematical problems in heat and fluid flow are still open owing to the complexity of engineering practice. With the help of the differential operators, e. g., classical, fractional-order, local fractional, and other operators, our chief aims of the special issue is to present more reasonable models for practical engineering problems in the area of heat and fluid flow, to develop some methods to find the approximate or exact, analytical or numerical solutions for the problems. The special issue titled Modern Mathematical Problems in Heat and Fluid Flow consists of 45 papers. It is divided into 3 main parts.