Baron Joachim Ammena van Plettenberg (8 March 1739, Leeuwarden, Netherlands – 18 August 1793, Zwolle, Netherlands) was the governor of the Cape of Good Hope from 11 August 1771 to 14 February 1785.
Plettenberg was presiding governor after Ryk Tulbagh's death.
On 18 May 1774 he was permanently appointed as governor.