Of special interest to geologists is the possibility of utilizing observations of symmetrical ripples preserved in rock strata to interpret the wave conditions of the ancient environment. This paper reviews the relationship between the wave action and the ripples produced. In shallow water with waves of low period and height, ripple lengths in sand in the 88-177 mu range are approximately a factor 0.8 of the orbital diameter of the water motion near the bottom just above the ripples. Such conditions exist principally in lakes and bays of limited fetch (and in wave flumes). In these environments the ripple lengths will tend to increase onshore in progressively shoalling water. Under oceanic conditions with longer period waves and deeper water, the water orbital diameter near the bottom is generally several times larger than the ripples produced. In this environment the ripples tend to decrease in length onshore. Graphs and computer programs are presented which aid in determining possible combinations of wave dimensions and water depths that could have generated observed oscillatory ripple marks.