This article is regarding fungible tokens; if you're looking for information on NFTs, see here.
For more basic information on tokens, see here.
MetaMask will show you any known standard ERC 20 tokens you own. They will all list under the Assets tab in Extension, or the TOKENS tab in Mobile. That said, sometimes your tokens will not display automatically (the ones that automatically appear are on our list of popular tokens here).
For those tokens that do not appear automatically, we have an easy step-by-step guide below on how to add it to your MetaMask:
How to Add a Token
If the token you're looking for isn't displayed automatically, just scroll down in Assets (or TOKENS) and press the ADD TOKEN button to add a new token, for example:
You would need the token's contract address, and you might also need to know the number of decimals that the token is tracked in (we usually auto-fill decimals if the token contract makes that possible). You can find that information on the Etherscan token page. Enter it in the form, then scroll down to click NEXT. On the next screen, confirm that you'd like to add the tokens to display on your account:
You can always remove the token later by clicking or tapping on it and pressing Hide (or, in Mobile, Remove).
If you don't know the address of the token you are trying to track, ask the person who sent you the tokens. The Ethereum blockchain has countless small tokens, so it's impossible for us to know all of them. If a person says you own tokens but hasn't given you an address, they haven't really given you the tokens, because, without the address, you don't have the information required to send or use those tokens yourself.
You can also view token balances on these block explorers: