As well as the one at 10 Downing Street in December, it'll look into an earlier one in November, and a Christmas do at the Department for Education.
MPs have suggested other parties may have taken place, including in the Prime Minister's flat, which he's denied.
Putney Labour MP Fleur Anderson has been asking these questions of the government in the Commons.
In response, Paymaster General Michael Ellis says that it’ll be fully investigated.