The microgrid is the new concept for efficient energy utilization through the energy storage systems and various technologies of producing energy such as high efficiency distributed generations, co-generators, and renewable energy resources. The optimal deployment of these elements brings the economic benefits such as low energy cost or emission. This paper reports the survey on existing research works on the optimal strategies for the operation of microgrids. In each case, the problem is discussed based on the single objective or multi-objective types of optimization. The optimization methods are also presented for the purpose of optimal operation of microgrids.