A Prohibited Transaction is an action you’re not allowed to take with your retirement account because it breaks IRS rules. These rules are meant to keep retirement savings tax-advantaged and used for their intended purpose. Common examples include borrowing money from your account, using it to buy personal items, or doing business with yourself or close family members through the account. If a prohibited transaction happens, it can lead to taxes and penalties, and in some cases, the entire account may lose its special tax treatment.