"Typical REM and NREM dreams are quite distinct, particularly with respect to episodic memory content. Episodic memory refers to knowledge about the past that incorporates information about where and when particular events occurred. It is typically contrasted with semantic memory, which consists of knowledge (e.g., facts, word meanings) that has been uncoupled from place and time, existing on its own (Tulving 1983Go). When examining REM sleep dreams for memory content, one finds that episodic memories are rare (see Baylor and Cavallero 2001Go) and typically emerge as disconnected fragments that are often difficult to relate to waking life events (see Schwartz 2003Go). These fragmented REM dreams often have bizarre content (Stickgold et al. 2001Go; Hobson 2002Go). For example, the normal rules of space and time can be ignored or disobeyed, so that in REM dreams it is possible to walk through walls, fly, interact with an entirely unknown person as if she was your mother, or stroll through Paris past the Empire State Building. NREM dreams, however, are quite different (Cavallero et al. 1992Go). Here, episodic memories do appear in dream content (see Foulkes 1962Go; Cicogna et al. 1986Go, 1991Go; Cavallero et al. 1992Go; Baylor and Cavallero 2001Go). Recent episodes are predominant, but remote memories occasionally appear as well. This pattern of results suggests to us that the memory systems needed to generate complete episodic retrieval are functional in NREM sleep but not in REM sleep.