A major theme is class divide. We see the wealthy elite living in East Egg, and those who are newly rich, like Gatsby, in West Egg. This divide creates a sense of tension and exclusion. The wealthy look down on Gatsby because he is 'new money', not born into their class. This class prejudice ultimately affects the relationships and fates of the characters.
The theme of illusion vs. reality is prominent. Gatsby has created an elaborate illusion around himself. His parties, his grand mansion, all are part of the facade he has built to attract Daisy. But in reality, he is still an outsider in the eyes of the old - money elite. The other characters also live in their own illusions. Daisy pretends to be happy in her marriage, when in fact she is dissatisfied. Nick is initially drawn into the glittering world of the wealthy, but gradually realizes the emptiness beneath the surface.