The theme of Jealousy
Othello is the most famous literary work that focuses on the dangers of jealousy. The play is a study of how jealousy can be fueled by mere circumstantial evidence and can destroy lives. (In Othello, the hero succumbs to jealousy when Iago convinces him that Desdemona has been an unfaithful wife – in the end, Othello murders his wife and then kills himself.) It is interesting that Iago uses jealousy against Othello, yet jealousy is likely the source of Iago's hatred in the first place. In Othello, jealousy takes many forms, from sexual suspicion to professional competition, but it is, in all cases, destructive.
The theme of Race
Othello is one of the first black heroes in English literature. A military general, he has risen to a position of power and influence. At the same time, however, his status as a black-skinned foreigner in Venice marks him as an outside and exposes him to some pretty overt racism, especially by his wife's father, who believes his daughter's interracial marriage can only be the result of Othello's trickery. Because the play portrays fears of miscegenation (the intermixing of races via marriage and/or sex), it's nearly impossible to talk about race in Othello without also discussing gender and sexuality.
The theme of Gender
Gender relations are pretty antagonistic in Othello. Unmarried women are regarded as their fathers' property and the plays two marriages are marked by male jealousy and cruelty (both wives are murdered by their own husbands). Most male characters in Othello assume that all Venetian women are inherently promiscuous, which explains why female sexuality is a huge threat to men in the play. Othello is easily convinced his wife is cheating on him and feels emasculated and humiliated as a result.
We should also note that it's impossible to discuss gender and sexuality without considering race - several characters in the play, including Othello, believe that black men sexually contaminate white women, which may partially explain why Othello sees his wife as soiled.
The theme of Sex
Shakespeare's play explores some much more common sixteenth century anxieties about miscegenation (interracial sex and marriage) by examining the relationship between a black man who marries a white woman, accuses her of being unfaithful, and then strangles her on her wedding sheets. In Othello, most male characters assume that all women are inherently promiscuous, which explains why all three women characters in the play are accused of sexual infidelity. It also explains, in part, why it's possible for Iago to so easily manipulate Othello into believing that his wife is having an affair. Othello is also notable for its portrayal of homoerotic desire, which seems to be a factor in Iago's plot to destroy Othello and Desdemona.
The theme of Marriage
Shakespeare's portrayal of marriage is pretty bleak in Othello. The play begins with a conflict between Desdemona's husband and her father, who sees his daughter's elopement as a kind of theft of his personal property. The plays two wives (Desdemona and Emilia) are both unfairly accused of infidelity, and both wives are murdered by their abusive husbands. More famously, perhaps, is the way Shakespeare examines sixteenth-century anxieties about interracial couplings in Othello, the marriage of a black man and a white woman allows Shakespeare to explore attitudes about race and gender.
The theme of Manipulation
Othello's villain, Iago, may be literature's most impressive master of deception. Iago plots with consummate sophistication, carefully manipulating Othello (without any real proof) into believing that Desdemona has been unfaithful. His understanding of the human psyche is phenomenal, as is his ability to orchestrate a complicated interweaving of pre-planned scenarios. Iago's deception is potent because of his patience, his cleverness, and what seems to be his intrinsic love of elegant manipulation.
The theme of Warfare
Since the play's protagonist is a military general, war is always hovering in the background in Othello. But the only actual battle the play promises is avoided, thanks to bad weather. The real battleground of the play, it turns out, is the mind. Many critics read Othello as an extended war allegory; it is possible to see Iago's machinations as the strategic planning of a general, individual victories as minor battles, and the three resulting deaths the casualties of psychological combat. The play also dwells on the relationship between masculine identity, war, and sexuality.
The theme of Hate
Hatred is supposed to have a cause, some concrete event or insult that inspires some sort of lasting rage. But in Othello, the plays villain is motivated by a hatred that seems to elude any reasonable definition. Iago's hatred and his determination to destroy his boss, Othello, seems out of proportion with the reasons he gives for it: anger that Othello did not promote him or jealously that Othello may have slept with Iago's wife. Iago's loathing has been famously called "motiveless malignancy" that redefines our understanding of hatred, making it seem a self-propelling passion rather than the consequence of any particular action.
The theme of Identity
In Othello, Shakespeare explores factors that play an important role in the formation's of ones identity - race, gender, social status, family relationships, military service, etc. Othello is also concerned with how an individuals sense of identity (which can break down and be manipulated by others) shapes his or her actions.