Guevara starts with a disclaimer: the text that follows is "not a story of heroic feats, or merely the narrative of a cynic," but rather "a glimpse of two lives running parallel for a time," his own life and that of his friend, Alberto Granado's (31).

He characterizes the book's contents: "In nine months of a man's life he can think a lot of things, from the loftiest meditations on philosophy to the most desperate longing for a bowl of soup–in total accord with the state of this stomach" (31).

The text, he indicates, relates a tale of adventure shaped by fate, and is the story of a change in Guevara's character: "The person who wrote these notes passed away the moment his feet touched Argentine soil again" (31). Thus, the Diaries are the story of a journey, but also the record of a transformation.

Guevara describes the genesis of his and Alberto Granado's travel plans.

The story opens on a morning around October 17, the Argentinean national holiday celebrating Juan Perón's 1945 release from prison. Drinking mate and talking about life while working on Granado's motorcycle, La Poderosa II, the two newly-unemployed friends spontaneously decide to drive the motorcycle to North America.