Mostly Third Person Omniscient; Occasionally First and Second Person
This narrator is shifty. No, he's not untrustworthy or scheming—he just seems to like to hop around.
When telling us about the Joads, this narrator is all-knowing and all-seeing. He dips in and out of each character's mind, knowing their immediate thoughts and fears.
However, interspersed with the chapters about the Joads are chapters that describe the historical context of the Dust Bowl and of the California migration. These chapters feature a diversity of perspectives and points of view. At times, the narrator with address the reader as "you." For example, he says,
For the quality of owning freezes you forever into "I," and cuts you off forever from the we. (14.4)
At times, we get to hear the inner monologue of a car salesman as he works to make a profit selling broken-down cars to poor families:
All right, Joe. You soften 'em up an' shoot 'em in here. I'll close 'em, I'll deal 'em or I'll kill 'em. Don't send in no bums. I want deals. (7.25)
So what's up with our ever-shifting narrator? We're not too sure. But we do know that by exposing us to a variety of perspectives and voices, Steinbeck allows us to really get a sense of what life was like for migrant workers in the late 1930s and of the various characters that played a role in this historical moment.
It's almost as though Steinbeck has created a textbook about migrant workers in California during the Great Depression, and he wants to represent as many stories as possible so that we can learn as much as possible.