We develope a relativeistic theory of clock syncronization that does not use or depend on a Newtonian framework or real time. Within the context of this theory, we focus on the problem of estimating the time on a remote clock. The concept of {\it rapport\/} is generalized to capture the situation when such an estimate is sufficient for clock syncronization purposes. With a single property, called the {\it Observable Drift Property}, we can characterize the information flow required for obtaining rapport. We compare our relativized and observable concepts with analogues based on the notion of real time in order to show that we are studying the right quantities. (Joint work with D. Dolev and R. Strong)