没关系。

You use this phrase primarily as a response. When someone says 对不起 (duì bù qǐ) for stepping on your toe, you say 没关系. It is short, sweet, and very easy to pronounce. You can say it once or double it up as 没关系，没关系 to sound extra comforting. If you want to sound more casual, you can even drop the 系 in some northern dialects, but stick to the full version for now.

Use it whenever someone apologizes for something minor. It works perfectly at a restaurant if a waiter forgets your water. Use it with friends if they are five minutes late for coffee. It is also great in the office when a colleague makes a small typo. It’s the 'don't sweat it' of the Chinese world. If you accidentally bump into someone on the subway, and they apologize, this is your go-to line.

Don't use 没关系 if someone is thanking you. That requires a different phrase like 不客气. Also, avoid using it for massive life disasters. If someone crashes your car, saying 没关系 might make you sound like a saint or someone who is incredibly rich and doesn't care about money. In very formal business negotiations, it might sound a bit too relaxed if a major contract term is missed. Stick to more professional language there.

Chinese culture places a huge emphasis on 'mianzi' or 'face.' When someone apologizes, they are admitting a fault, which can be awkward. By saying 没关系, you are effectively 'giving face' back to them. You are signaling that the harmony of the group is more important than the minor inconvenience you suffered. It’s a verbal handshake that restores social balance instantly.

In Taiwan, you might hear 没关系 pronounced with a slightly different stress. In mainland China, you’ll often hear 没事 (méi shì), which literally means 'no matter' or 'it’s nothing.' 没事 is the cooler, younger cousin of 没关系. If you want to sound like a local in Beijing, add an 'r' sound at the end: 没事儿 (méi shìr). It makes you sound instantly more relaxed and approachable.