This paper reviews the present state of heat transport devices of the oscillating-flow type. First, outlines of uses, required characteristics and desirable new functions of heat transport devices are given. Next, heat transport devices are categorized into some groups based on the principles of enhanced heat transport. Finally, the present state and remaining issues of oscillating-flow heat-transport devices such as SEMOS (Self-Exciting-Mode Oscillating-Flow) and COSMOS (Counter-Stream-Mode Oscillating-Flow) heat pipes are summarized.