We consider the the problem of tracking heavy hitters and quantiles in the distributed streaming model. The heavy hitters and quantiles are two important statistics for characterizing a data distribution. Let A be a multiset of elements, drawn from the universe U = {1, . . . , u}. For a given 0 1, the -heavy hitters are those elements of A whose frequency in A is at least |A|; the -quantile of A is an element x of U such that at most |A| elements of A are smaller than A and at most (1 - )|A| elements of A are greater than x. Suppose the elements of A are received at k remote sites over time, and each of the sites has a two-way communication channel to a designated coordinator, whose goal is to track the set of -heavy hitters and the -quantile of A approximately at all times with minimum communication. We give tracking algorithms with worst-case communication cost O(k/ ? log n) for both problems, where n is the total number of items in A, and is the approximation error. This substan...