  We classify the supersymmetric mass deformations of all the super Yang-Mills
quantum mechanics, which are obtained by dimensional reductions of minimal
super Yang-Mills in spacetime dimensions: ten, six, four, three and two. The
resulting actions can be viewed as the matrix descriptions of supermembranes in
nontrivial backgrounds of one higher dimensional supergravity theories. We also
discuss the utmost generalization of the light-cone formulation of the
Nambu-Goto action for a p-brane, including time dependent backgrounds.
