We propose a framework for temporal quantum theories for the purpose of des
cribing states and observables associated with extended regions of space-ti
me quantum mechanically. The proposal is motivated by Isham's history theor
ies. We discuss its relation to Isham's history theories and to standard qu
antum mechanics. We generalize the Isham-Linden information entropy to the
present context. [S1050-2947(99)07902-0].