This dissertation deals with Conceptual Metaphor Theory and Experientialist philosophy by George Lakoff and Mark Johnson and Existentialist philosophy by Jean-Paul Sartre. In the first chapter we study Lakoff and Johnson s works on Metaphor (1980, 1999) and we also analyse the most important revisions, extensions and criticisms related to the theory. In the second chapter we make a comparison between experientialism and existentialism by means of the concept of imagination a key component of both theories. In the third and last chapter we examine the central metaphors that are revealed in the most important book of existentialism: Jean-Paul Sartre's (1943a) L'être et el Néant. As if it were another chapter in Lakoff & Johnson (1999) we will pay attention to this very important book of Sartre's in order to discover which metaphors sustain his system. The analysis will be based on Lakoff & Johnson's Conceptual Metaphor Theory and Lakoff & Johnson's (1999) key idea that metaphor is an essential skill that allows us to build philosophical systems. Finally, in a concluding section we will summarize the key proposals defended throughout this work.