One of the central themes in Richard Matheson's I Am Legend is man's will to survive. Each day, protagonist Robert Neville undertakes the task of protecting himself from the vampire plague. He mends sections of his house that have been damaged by the previous night's vampire attack; collects items of defense, such as garlic; and makes stakes. Each day, he collects and burns the bodies of the deceased and drives stakes into the hearts of newly claimed victims to prevent the formation of new vampires. Matheson portrays the theme of the will to survive early on in the novel when, as Robert reflects how gloomy his house has become since the windows have been boarded up and how running three air conditioning units is necessary to make the house livable, he says to himself, "A man could get used to anything if he had to." The ability to "get used to anything" show man's ability to survive.
A second central theme in the novel is the vulnerability of human life. This theme is of course portrayed through the vampire plague but also through references to Robert taking care of himself, such as grooming his teeth. In addition, the theme is portrayed through images of death. For example, after Robert boards up all the windows of his house, he reflects that doing so "had made the house a gloomy sepulcher," which is another word for tomb or grave.