The present capability to acquire, process and display very large sets of high-quality magnetic survey data has far outstripped the capacity to extract all the geological information from the data. Interpretation of magnetics has lagged behind, largely because of a lack of information on magnetic properties within the survey areas and because the geological factors and processes that determine magnetic signatures are often poorly understood. In the absence of magnetic property measurements, simplistic rules-of-thumb concerning magnetic properties of different rock types can be deceptive. Furthermore, empirical correlations between mapped geology and magnetics in one area cannot necessarily be extrapolated to other areas of poor exposure if changes in depositional environment, metamorphic grade or structural setting are ignored. Magnetic modelling is afflicted by the inherent non-uniqueness of source geometry. Information on magnetic properties in the area of interest is important for constraining interpretation in order to resolve this ambiguity. Magnetic petrology integrates rock magnetism and conventional petrology in order to define the processes that create, alter and destroy magnetic minerals in rocks. By relating magnetic mineralogy, bulk magnetic properties, petrology and geochemistry to observed magnetic anomalies an understanding of the geological factors that control magnetic signatures is obtained, which can be used to improve geological interpretation of magnetic surveys.