Mesoporous silica nanoparticles (MSNs), with their intrinsically large and easily functionalized surface areas and pore volumes, are particularly well-suited to efficient conveyance of a wide variety of therapeutic agents. When combined with other organic/inorganic nanomaterials, the resultant organic/inorganic-MSN hybrids demonstrate unique synergies and even greater versatility. In this paper, we describe the current status and future prospects of MSNs and organic/inorganic-MSN hybrids for combined therapeutic and diagnostic - theranostic - biomedical applications.