French Onion Soup (French: soupe à l'oignon) is a soup based primarily on onions (which may be caramelized or plain) and beef broth. The soup is usually served with croutons and cheese as toppings.

Although the soup is perhaps one of the oldest recipes in existence, dating as far back as perhaps the Roman Empire, it did not gain widespread popularity in the US until the 1960s when a ressurgence of French cooking swept over the country. In the US, it is often served completely covered with melted gruyère cheese and baguette-style bread. It may be altered to include vegetable broth for vegetarians and may be served without cheese for vegans.