This paper describes the systematic variations in size and quality of diamonds that result from transport by fluvial and marine processes. It is shown that diamonds originating in rather restricted source areas can be spread across many tens of thousands of square kilometers. Downstream or alongshore transport can be followed for several hundred kilometers, with a systematic reduction in average diamond size accompanying such transport. The diamond size distribution is progressively modified with increasing travel distance, and the quality of the diamonds improves as inferior types are destroyed. The accompanying variations in crystal form are outlined. Certain implications for exploration programs are mentioned.