We demonstrate that temporal observables, which are sensitive to a system's
history (as opposed to its state), implicate entangled histories. We exemplify
protocols for measuring such observables, and algorithms for predicting the
(stochastic) outcomes of such measurements. Temporal observables allow us to
define, and potentially to measure, precise mathematical consequences of
intrinsically disjoint, yet mutually accessible, branches within the evolution
of a pure quantum state.