Rear admiral is a senior naval flag officer rank, equivalent to a major general and air vice marshal and above that of a commodore and captain, but below that of a vice admiral.

The term originated in the days of naval sailing squadrons and can trace its origins to the Royal Navy. Each naval squadron was assigned an admiral as its head, who commanded from the centre vessel and directed the squadron's activities. The admiral would in turn be assisted by a vice admiral, who commanded the lead ships that bore the brunt of a battle. In the rear of the squadron, a third admiral commanded the remaining ships and, as this section was considered to be in the least danger, the admiral in command of it was typically the most junior. This has continued into the modern age, with rear admiral the most junior admiralty of many navies.

In most European navies, the equivalent rank is called counter admiral.