A steep rainfall gradient exists across the Namib Desert in southern Africa, which is unique in that frequent coastal fog occurs in areas that receive the least rainfall. Overall, the Namib is hyper-arid in terms of rainfall (25-100mm mean annual rainfall, MAR), but areas within about 60km of the coast see up to 100 days of fog each year. This scenario has influenced the distribution of plant species and the behavior of Namib fauna. In this study, carbon and nitrogen isotopes are used to investigate the biogeochemistry of vegetation the Namib aridity gradient, and fog uptake by individual plants is estimated by comparing water isotopes (delta2H and delta18O) of fog, groundwater, rain, soil water and plant water. Using the natural aridity gradient as a basis for this investigation allows for observation of patterns that can potentially be related to controlling biogeochemical processes. Studies of carbon and nitrogen isotopes in vegetation along precipitation gradients have revealed similar patterns in the Kalahari of southern Africa and in West Australia. The Kalahari trend observed along a precipitation gradient of 200-1000mm MAR shows enriched delta13C values in drier areas, and this trend is only apparent in C3 vegetation. The West Australia gradient (150 to >1000mm MAR) follows the same general pattern, but the values are quite variable below about 250mm MAR. The corresponding nitrogen isotope data in the Kalahari shows an enrichment in 15N with less rainfall, again only apparent in C3 vegetation. Although there are significant differences between the Namib and Kalahari setting - notably soils and climatology - the Namib aridity gradient could potentially extend the Kalahari data set to areas that receive less than 100mm MAR. The fog and the unique survival strategies of Namib plants may explain differences between the Namib and Kalahari patterns. For example, the C3/CAM species W. mirabilis has highly variable delta13C values (-17.5 to -240/00), with a slight enrichment corresponding to lower rainfall and higher fog occurrence. To further investigate the relationship between aridity and the delta13C and delta15N patterns, ten common plant species are grouped according to fog utilization as estimated from delta2H and delta18O of extracted plant water.