In this chapter we will focus primarily on the promise and limitations of the ocean crust as a recor- der of geomagnetic field variations, emphasizing the record of past geomagnetic field variations recorded in anomalies (and therefore in source magnetization) on timescales of 103 years (excursions) to 104–106 (reversals) and 107–108 (superchrons). We review the origin of the magnetization in the various crustal source layers responsible for lineated magnetic anomalies and conclude by mentioning some appli- cations to deciphering how oceanic crust formed and by speculating on future directions. The chapter is based mostly on published literature that appeared since the last major review of ocean crust magnetiza- tion by Smith (1990).