The utilization of mixed consortia or mixed culture has become a current research trend of applied microbiology, bioprocess engineering and biotechnology. The constituent microorganisms of such mixed cultures can jointly perform complex processes efficiently, yielding the desired product at an augmented rate, in comparison to monocultures. It is understandable that the interactions between the microbial partners in these mixed cultures are expected to have a significant impact on the combined performance of the microorganisms and the bioprocess as a whole. Prevalence of positive interactions (commensalism or mutualism) among microbial members of a mixed culture or consortia can significantly enhance the product outcome of the bioprocess, ensuring their industrial application and long-term stability. On the contrary, negative interaction (parasitism, predation or ammensalism) leads to elimination of microbial members from the consortia causing the destruction of community structure as well as disruption of cumulative performance. Therefore, a priori knowledge on the type of interaction between the microorganisms is also essential for the optimization of the performance of the designed consortia. This could only be achieved through the study of inter-microbial interaction prevailing in a mixed culture. In the present article, different bioprocess applications of mixed cultures, currently in practice along with types of positive microbial interactions involved, have been reviewed. Complexity of mixed cultures from the perspective of multiple types of intra-culture relationships has been explained in detail. Overall, the necessity for more in-depth research studies on "microbial interaction" in mixed culture bioprocesses has been stressed in the article.