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Summary The magnetic study of rocks leads to three broad fields of knowledge. The first is the history of continental movement as deduced from magnetic rocks, and the comparison of palaeomagnetically determined ancient latitudes with palaeoclimatological evidence. These areas are reviewed quite briefly. The second field is the history of the earth's magnetic field itself. This concerns the dipole or non-dipole nature of the ancient field, its intensity variations, and reversals of its polarity. The third field is the solid state study of the magnetic minerals responsible for the record contained in the rocks. In particular, one is interested in possible “self-reversals” of polarity of natural magnetization, and in the mechanisms by which various kinds of remanence are achieved—isothermal, thermo-remanent, and chemical remanent magnetizations, and viscous magnetizations slowly acquired in weak fields. Oxidation and exsolution phenomena in iron-titanium oxides are also of interest because of possible influences on the natural magnetization.