In the Indo-Pacific Ocean, 28 species of anemonefish are known to associate with ten species of sea anemones. It has long been a matter of interest to many researchers that different species of anemonefish use different host anemones. Anemonefish in nature face predation pressure, so they need to choose hosts that can serve as high-quality shelters and have low energy consumption costs. Different species of anemonefish differ in their sizes, in their resistance to cnidarian venom, and in their tolerance to environmental conditions, which may lead to resource partitioning among species. In this chapter, we reviewed studies on host utilization by anemonefish and concluded that, on an evolutionary scale, anemonefish divide resource utilization by altering the host species or environment for each species. However, studies from the Ryukyu Archipelago revealed that host selection was plastic on a regional scale, depending on the density of each species of anemonefish. Furthermore, the loss of coastal habitat influences the species compositions and densities of host anemones and anemonefish, which in turn may influence host selection by anemonefish. In order to understand the distribution ranges and limiting factors of each species of anemonefish, and to protect them from human-induced environmental degradation, we need to better understand the selection of hosts and environments by each species of anemonefish.