What are the themes of Shakespeare's Othello?

Most obviously, the play is about jealousy and the damage
that jealousy can do to a relationship.  In the play jealousy is a "green eye monster
that mocks the meat it feeds upon."  At the heart of the play, we have two jealous men,
Iago who is jealous because he is jealous, and Othello, is becomes inflicted with the
"poisonous mineral" because of Iago's lies and
machinations.

But the play is also about the way men view
women:  the tendency to view women as prizes that are won, and women's infidelity as
attacks on their pride.  This inability to see women truly without generalization and
without stereotyping is a central idea of the
tragedy.

Another theme is the insider/outsider theme.
 Othello's race, while not a factor in his achieving prestige as a military man, makes
him feel insecure in his marriage.  "Haply for I am black" Othello cries, and when
comparing himself to Cassio, who is one of the "curled darlings" of Desdemona's country,
he feels as if he has lost her.  Part of Iago's manipulation of Othello is to make him
feel as if he is an outsider to Venetian society.

And of
course as is common with Shakespeare, the play explores the appearance versus reality
idea.  "When devils with the blackest sins put on, they do at first with heavenly shows
as I do now," Iago boasts.  Iago, clearly the devil of the play, is seen by every major
characters as honest, honorable, and trustworthy.  Desdemona, who is clearly the angel
of the play, is viewed as deceitful and ungrateful by her father and a whore by her
husband.