Many situations involving single-phase convection at cryogenic temperatures can be solved using techniques that are applicable at conventional temperature levels. One interesting problem in many cryogenic systems is heat transfer in the near-critical region. This condition is not difficult to achieve because the critical pressure for hydrogen, for example, is only 12.98 atm (1315 kPa or 198 psia). In this chapter, general problems involving singlephase convection and special problems involving heat transfer in the near-critical region will be considered.