The Long Voyage by Jorge Semprun is a cerebral narrative that has several themes. One of the most prominent themes—which is evident from the first sentence of the story—is human suffering. The unnamed narrator describes in vivid detail the miserable conditions inside a train boxcar crammed with 120 men. They are prisoners of war from France.

The narrator is a Spanish communist who joined the French underground resistance guerrilla group, Maquis. This introduces the second theme of the book, which is war. The suffering of people described by the narrator gives a human face to the political nature of war. The other theme is oppression, specifically by fascist governments. Not only does the narrator have to survive the brutal programs of Nazi Germany, but has also experienced fascism in his homeland of Spain during the reign of Franco.

Due to the fact that the story revolves around World War II in Europe, the theme of xenophobia is also present throughout the story. Jews are methodically kidnapped, imprisoned and murdered. The narrator's Jewish friends begin to disappear and are killed by the German forces.