The vast bulk of Facebook's revenue comes from advertising. The company's total advertising revenue in Q3 2021 was $28.2 billion, which was up compared to 2019 This increase came about, despite a decrease in advertising revenue in March 2020, due to Coronavirus. The importance of advertising to Facebook is evident when you see that of that $17.74 billion revenue, $17.44 billion comes from advertising with only $297 million in other income.