The numismatic collection comprises coins, tokens, medals and related objects. It ranges widely, from ancient times to the present, with five main areas of strength: Celtic coins, Greek and Roman coins, coins of England and the British Isles, tokens, banknotes and 'paranumismatica', primarily Welsh, and commemorative medals and awards, especially relating to Wales and the exploits of Welsh people. There are also small comparative collections of European, British Colonial and World coins.

The collections includes numerous hoards, archaeological site finds and single coin finds from the Roman period onwards. Coins found in or relating to Wales remain an important element of current collecting. Occasional Welsh finds of treasure, such as the English Civil War hoard from Tregwynt, Pembrokeshire (buried around 1648 and rediscovered in 1996), provide spectacular individual acquisitions.