The Tortilla Curtain is a novel dealing with the disconnect between the Mexican and U.S. cultures, and the title needs to be understood in its historical context.

During the Cold War the term "Iron Curtain," coined by Winston Churchill, referred to the boundary between Eastern Europe—at that time the Soviet Union and its "satellite" countries such as Poland, Hungary, and East Germany, upon which communism had been imposed by the Soviets—and the democratic Western European states (West Germany, France, Britain, and so on). The boundary was both a physical and an ideological one, and was a barrier across which many Eastern Europeans attempted to flee in order to escape communism and reach the democratic West. The policy of the Soviet bloc countries was in effect to keep their citizens imprisoned and to forbid immigration to the West, and hundreds of kilometers of barbed wire and other physical barriers such as the Berlin Wall were set up to prevent people from escaping the communist states.

T. C. Boyle, in transmuting "iron curtain" into "tortilla curtain," is analogizing this communism-democracy dichotomy with the divide between Mexico and the United States. Just as people fled the communist countries during the Cold War, people leave Mexico for the United States in search of jobs and a better mode of living. But the larger point is that the split between the latino and U.S. cultures exists within the States, since in the novel Candido and America live practically adjacent to the Mossbachers in the Los Angeles area, but under completely different economic conditions. So a curtain exists as both a physical border between Mexico and the U.S., and as a cultural divide among people of different ethnicity—just as, during the Cold War, there was both a physical and ideological divide between Communism and the "Free World."

The tortilla is representative of the Mexican experience, and a curtain is something that separates or divides.  The "tortilla curtain" refers to the physical boundary between Mexico and Southern California, and, in a deeper sense, the vast ideological and sociological chasm separating the American citizen and the Mexican immigrant.

The two central characters in the story are Delaney Mossbacher and Candido Rincon.  The two men and their families live in close proximity, but their lives are completely different.  Delaney has a nice house, two cars, and is financially secure, while Candido lives in a makeshift hut made of garbage and discards, and must struggle everyday just to survive.  Although Delaney considers himself to be open-minded and liberal, his philosophy works better in theory than in practice, and when faced with the reality of Candido's presence and need, he discovers that he is more inclined to look the other way and gate himself off from what feels like an intrusion.  At the end of the story, both Delaney and Candido find their lives threatened by a flash flood.  It is only through sharing this dire experience that the men are able to break through the "tortilla curtain" and discover their common humanity .