In this project we investigated how to measure naturally occurring radioactive materials (NORM) using gamma spectrometry. We chose to study radionuclides from the natural decay series: the uranium, actinium and thorium series. We suggested nuclides that were relevant to measure and, among those, which could be measured using gamma spectrometry. We measured twelve samples using two methods: one for screening and one for quantification. The screening method used the sample's internal 228Ac for calibration, and could therefore be applied on uncalibrated geometries. By using internal calibration the results were relative and were therefore given in nuclide ratios. A limited selection of gamma lines, chosen since they are free from interferences as well as true coincidence summing (TCS), was used in both methods. The sensitivity of the quantification method was compared to two other measurement techniques: ICP-SFMS and alpha spectrometry. Furthermore, we mathematically described the dynamics of the successive radioactive decay in the series. The dynamics generates radioactive equilibria and we presented the most important ones. We also discussed the possibility of naturally occurring disequilibria. By understanding the dynamics we made a recommendation on how to properly correct the measured nuclides by decay