Degradation is weakening of a material within a structure with time. Degradation mechanisms can result in metal loss (as uniform or localised attacks), cracking or changes to the material properties (e.g. increased brittleness). In addition, damage from impact and other high loads  may cause the material to be more vulnerable to degradation and can also lead to changes in geometry of the structure or structural parts. This chapter describes the main degradation mechanisms that affect materials within offshore structures, together with how their effects  can be detected and remediated. Finally, a summary is provided of the main considerations to be taken into account when assessing materials in an ageing offshore structure for life extension.