The requirements of thermal management in aerospace applications are continuously growing, whereas the allotments on weight and volume remain constant or shrink. To meet the high heat flux removal requirements, compact, high-performance, and lightweight heat transfer equipment are needed. Heat exchangers based on microchannels are very suitable, as they offer opportunities for high heat flux removal because of their good thermal performance and extremely compact size. However, aerospace challenges include reduced gravity or microgravity, low or no atmospheric pressure, extreme temperatures, aerodynamic heating, dynamic vibration, shock loads, and extended duration of operations. Also alternative power sources are needed for aerospace vehicles, e.g., fuel cells. As hydrogen is the common fuel, efforts have been spent on its production, transportation, storage, system design, and safe and effective handling. Heat transfer issues are also demanding challenges for aerospace propulsion. It is important to protect the propulsion surfaces from the hostile thermal environment. One way to achieve this is to develop materials capable of withstanding the hostile environment and offering an adiabatic surface that will not melt or lose its structural integrity. Another approach is to immediately cool the exposed surfaces. Heat transfer issues in hypersonic flights include very high aerodynamic loads, laminar–turbulent transition, shock/shock and shock/boundary layer interactions, film cooling and skin friction reduction, advanced composite materials, combined thermal/structural analysis, real-gas effects, and wall catalysis, as well as thermal management of the integrated engine–airframe environment. Heat pipes are potential candidates for passive cooling of structures exposed to very high heat flux levels. It is obvious that heat transfer engineering and thermal sciences are important for the design and development in aerospace applications.