Brane Descent Relations in M-theory

We discuss how the BPS branes of M-theory could be described as bound states of non-BPS M10-branes. This conjectured M10-brane is constructed as an unstable spacetime-filling brane in the massive eleven dimensional supergravity defined with a Killing direction, such that 1) the BPS M9-brane is obtained after the tachyonic mode of an M2-brane ending on it condenses, and 2) it gives the non-BPS D9-brane of the type IIA theory upon reduction. The existence of other non-BPS M-branes is also discussed, together with their possible stabilisation within the Horava-Witten construction.