This paper explores Hemingway`s existential individualism in For Whom the Bell Tolls that is based on the interdependency of human beings because the individual cannot become human by himself. For existentialists, an individual is never isolated from the others; yet he as an authentic form of true being commits himself to the action and takes responsibility of his own decision. For the individual who commits himself to the action, his whole existence depends on his decision at the present moment. Even though his existence should remain in the relationship with the others, the only way with which the individual stands against nothingness of the universe is to commit himself to the action. Hemingway as an existential writer presents Robert Jordan who appears as a "functionary" to complete his mission to destroy a bridge in Spain. Yet Jordan witnesses the voidness of the world at war and finds himself lost without any exit to escape from the world. His sexual relationship with Maria, however, gives him an insight of the significance of "now" as well as the possibility of individual salvation through his sexual relationship with Maria. As Jordan realizes that life is made up of infinite sequence of "now" and that he should commit himself to action at the present moment, he decides to sacrifice himself and confront death when his leg is broken. This decision is made not only for the guerilla including Maria to escape from the chase of the Fascist but for himself because he realizes that there is only one way of assuring his existence: a fully committed action against death. Hemingway in the novel emphasizes that the individual should value the present moment which gives the possibility of personal salvation from the voidness of the universe and that he should commit himself to action with his own will. Hemingway`s hero therefore becomes a man who gains his authenticity of being and whose existence is in the action.