GO:0003158

The process whose specific outcome is the progression of an endothelium over time, from its formation to the mature structure. Endothelium refers to the layer of cells lining blood vessels, lymphatics, the heart, and serous cavities,and is derived from bone marrow or mesoderm. Corneal endothelium is a special case, derived from neural crest cells. [GOC:mtg_heart]