We attribute similarities in the rheology of many soft materials (foams, emulsions, slurries, etc.) to the shared features of structural disorder and metastability. A generic model for the mesoscopic dynamics of ''soft glassy matter'' is introduced, with interactions represented by a mean-field noise temperature x. We find power-law fluid behavior either with (x<1) or without (1<x<2) a yield stress. For 1<x<2, both storage and loss modulus vary with frequency as omega(x-1), becoming flat near a glass transition(x=1). Values of x approximate to 1 may result from marginal dynamics as seen in some spin glass models.