Moodys, one of the big three credit ratings agencies, has cut its outlook for the UK economy from stable to negative.
Credit rating agencies, in essence, rate a country on the strength of its economy.
More specifically, they score governments (or large companies) on how likely they are to pay back their debt.
A rating affects how much it costs governments to borrow money in the international financial markets. In theory, a high credit rating means a lower interest rate (and vice versa).
This is because of concerns at the impact that leaving the European Union may have on the UK economy. Moodys warned that the referendum result may have negative implications for the countrys medium-term growth outlook.