During its life cycle, the tree-killing mountain pine beetle Dendroctonus ponderosae Hopkins interacts with phoretic organisms such as mites, nematodes, fungi, and bacteria. The types of associations these organisms establish with the mountain pine beetle (MPB) vary from mutualistic to antagonistic. The most studied of these interactions are those between beetle and fungi. The least studied are interactions with bacteria, but these have received increased attention recently. Nematodes remain little studied. We reviewed the significant literature pertaining to MPB phoronts. A number of potentially important interactions and contributions resulting from associations between MPB and its phoronts are discussed. A wealth of literature exists on this topic, yet many questions remain unanswered, and the effects of some phoronts on population levels remain unexplored.