Nanofillers have attracted significant attention in recent years due to their remarkable mechanical, thermal and electrical properties, rendering them as ideal fillers for advanced polymer composites. However, due to strong interparticle interactions, individual nanofillers tend to form micrometer-size bundles which entangle and condense into larger agglomerates with inferior properties. Difficulties in uniformly dispersing nanofillers have resulted in sub-par material properties as compared with what could theoretically be achieved for well-dispersed systems. In other words, the material properties of nanocomposites are controlled by the state of nanofiller dispersion in the polymer matrix and nanofiller/polymer interfacial interactions. In this presentation we evaluate different methods to characterize the state of carbon nanotube and cellulose whiskers dispersion in different media and at different length scales. We also examine potential means to control interfacial interactions filler/medium by appropriate selection of dispersing agents.