Messenger, WhatsApp and Instagram.
The new feature launched by Facebook - who own all of the above apps - in the US this week means people will be able transfer money to friends, shops, and also donate to causes.
The company has stated that it's separate from the Facebook's new Calibra wallet and the Libra network, and "built on existing financial infrastructure and partnerships".
At launch, Facebook Pay will only enable users to make in-app purchases and transfers, but will eventually come to Instagram and WhatsApp.
Deborah Liu, Facebook's Vice President of Marketplace and Commerce, said: "Over time, we plan to bring Facebook Pay to more people and places, including for use across Instagram and WhatsApp."
Pay will be accessible from the settings tab of Facebook and Messenger.
It is supported by PayPal, Stripe and all major debit and credit cards.
There is no official date for when it will be available in the other apps.