This essay aims at defining to what extent our friends are involved in our personal identity. Our thesis is that friends share a common identity which occupies a larger or smaller part of their personal identity, depending on the depth of their relationship. Yet, friendship does not merely consists in the shaping of ourselves: as it appears more obvious, we remain separate entities and my friend can help me in the understanding of my own self thanks to what he has (...) learnt in our intimate and long-lasting relationship. The other consequence of this individuation is that friendship is based on a metaphysical desire which cannot be fulfilled: I will never be able to feel exactly what my friend feels, even if I rationally come close to it by sharing his life. (shrink)