Platelet ageing can refer to how platelets generally change as people age, or how individual platelets age as they circulate within an individual; in both instances, significant differences have been noted. Despite some contradictory data, most literature demonstrates that platelet count declines as people age, accompanied by changes in the platelet transcriptome and proteome. These changes are associated with alterations in metabolism and enhanced platelet activation both basally and following stimulation, which may contribute to the increased risk of thrombosis reported in older people. Exploring the second meaning of platelet ageing, research has shown that as individual platelets age within the circulation, there are extensive associated changes in composition, including the transcriptome, proteome and subcellular structures. These changes are accompanied by a circulatory age-related reduction in haemostatic function. These insights into the functional changes occurring as platelets age in the circulation, along with novel methods to study these processes, can be coupled with research in aged people to provide a more extensive characterisation of platelet composition and function, and how these alterations may be related to increased risks of thrombosis and cardiovascular disease.