Chapter 8 gives an overview of the general structure and composition of oceanic lithosphere – the most common type of lithosphere on Earth. Its thickness, layered structure, seismicity, variation in seafloor elevation, magnetic anomaly pattern and composition are put in context of oceanic spreading and associated processes. The range of spreading rates, from ultraslow to superfast, is discussed. Differences in spreading rate have implications for the size of the magma chamber under the spreading ridge and therefore for the thicknesses of the different oceanic crustal layers. Slow spreading also favors exhumation of mantle and the formation of extensional detachments and core complexes. In this chapter the crystallization of melt to form oceanic crust is discussed along with the formation of hydrothermal mineralization and smokers. Hydrothermal activity produces ores that represent important metal resources that may be mined in the future. This chapter also presents ophiolites, oceanic crust on land, and simple models for obduction.