The Finnmarka complex, one of the younger, shallow Permian intrusive bodies within the Oslo graben, crops out over about 130 square kilometers as a highland area 40 kilometers west of Oslo, Norway. The complex is composed of akerite, granodiorite, and granite. The granitic core forms the bulk of the mass. New petrographic, mineralogical, chemical, and X-ray data have been accumulated in an attempt to understand the environment in which the complex formed and the interrelationships between the rocks units. At all observed localities the three units are in sharp contact with one another and with the sedimentary host rocks. None of the contacts show features suggestive of dislocation or chilling. Attention has been focused on the feldspar phases of the three rock types because they are of unusual complexity and give insight into the development of the complex. The akerite contains two plagioclase phases in reaction relationship, and the granodiorite is rich in early-formed oligoclase. Both of these units contain late alkali feldspar as selvages and interstitial fillings. The one-feldspar granite contains a coarse perthite and approximates a residual albite-orthoclase-quartz liquid in composition. Powder and single-crystal X-ray studies of perthites from the granite and granodiorite show that they are essentially of the low albite-orthoclase variety. Heating experiments reveal unusual compositional trends during perthite homogenization. Indications are that the complex was intruded within a relatively short time interval at temperatures in the range 660°-900° C. The total pressure under which crystallization took place was probably no more than 500-1,000 bars.