The probe will investigate matters such as whether these big companies have an unfair and unsustainable monopoly over their respective markets.
"Without the discipline of meaningful market-based competition, digital platforms may act in ways that are not responsive to consumer demands," said Makan Delrahim, assistant attorney general of the US antitrust section.
The Justice Department said that it will be conferring with and taking information from members of the public, including industry participants with significant insight into these matters.
The probe will operate separately to previous probes into Google and Apple, focusing instead more generally on the big players in the digital landscape.