Phonolites of Tertiary age occur as eroded tholoids, lava flows, ignimbrites, and coulees in the Klinghardt Mountains of southern Namibia. Sixty samples have been analyzed for major and trace elements and fourteen of these for . The phonolites lie close to the low-pressure cotectics in Q-Ne-Ks, in keeping with their petrography which indicates that most samples have phenocrysts of both nepheline and sanidine. Na has been variably lost from the rocks during crystallization and devitrification/alteration of hypocrystalline specimens. The concentrations of other elements except perhaps LREE remain unaffected. The composition variation within the phonolites is consistent with fractional crystallization of nepheline, sanidine, and minor clinopyroxene to produce a number of near-parallel lineages from similar, but not identical, parent compositions. Fractional crystallization results in increasing SiO2, Na2O, Zr, Nb, Ce, Rb, Th, Y, Zn, Pb, and REE, but decreasing K2O, TiO2, CaO, MgO, P2O5, Ba, and Sr with differentiation. Enrichment factors for Zr and Nb indicate that the most evolved phonolites represent 20% residual liquids, a result which is consistent with major element modelling. In the evolution of the most differentiated phonolites fractional crystallization was accompanied or followed by volatile transfer causing depletion of Th, Y, LREE, Zn, and Pb relative to Zr and Nb. Initial for most of the phonolites lie in the range 0.7050-0.7057, rising to 0.7080 in the low-Sr samples. This is suggestive of some interaction with crustal rocks, but this interaction has no detectable influence on the fractionation controlled compositional evolution of the suite. The phonolites are associated on a regional scale with nephelinite and melilitite rocks but there is no favourable evidence for an evolutionary link between these and phonolite. Alternatively, the primitive phonolites may have originated through anatexis of metasomatized, nepheline-normative crustal rocks.