This paper considers the problem of estimating the offset in timing of like events at geographically separated locations as a basis for establishing common knowledge of time and, hence, system synchronism. Configurations discussed involve interrogation and reply between a user and a single donor, and one-way propagation between a user and the multiple sites of a reference system. The latter category includes navigation systems, which are shown to be appropriate means for disseminating time. Further ramifications of time dissemination are discussed, including the characteristics of clocks suitable for airborne application. Variables and their relationship and solution are defined for stationary and moving users, and for users of atomic and crystal clocks. For the case in which frequency is offset between clocks, as is likely when crystal oscillators are used, methods are described that permit the estimate of offset in frequency as well as in time. Recursive minimum-variance methods are examined in some detail, and a parametric analysis of performance relative to random and systematic sources of error is given.