The Universality of M-branes

We review the evidence for the various dualities amongst the five D=10 superstring theories and for the existence of M-theory using the associated effective supergravity theories. We also summarise the combinatorial technics developed for constructing BPS solutions in D=11 supergravity theory and conjecture that all the BPS solutions of D<11 supergravity theories can be derived from the BPS solutions of D=11 supergravity that preserve 1/2 the supersymmetry. To demonstrate this, we derive the dyonic p-brane solutions from eleven dimensions.