The moduli spaces M_k of SU(2) monopoles on R^3 of charge k are among the oldest studied objects in gauge theory, yet open questions still remain, such as Sen's conjecture for their L^2 cohomology. I will discuss compactifications of these moduli spaces as manifolds with corners, with respect to which their hyperKahler metrics are of "quasi fibered boundary" (QFB) type, a metric structure which generalizes the quasi asymptotically locally euclidean (QALE) and quasi asymptotically conic (QAC) structures introduced by Joyce and others. This geometric structure, which is best understood by comparison to the simpler moduli space of point clusters on R^3, systematically organizes the various asymptotic regions of the moduli space in which charge k monopoles decompose into widely separated monopoles of charges summing to k. This is joint work with M. Singer and K. Fritzsch.