Multilevel inverters (MLIs) are being used in wide range of power electronics applications. These converters that are attracted a lot of attentions during recent years have different topologies with similar basic concept. This paper presents five main submodules (SMs) that are used as the basic structures of MLIs. The paper reviews the common multilevel inverter topologies with the structural point of view. The topologies are divided to main SMs to show conventional MLIs configuration and future topologies that can be created from the main SMs. The comparative study on topologies is investigated with details. The MLIs are categorized and investigated with due attention to some indexes such as the number of components, the ability to create inherent negative voltage, working in regeneration mode and using single DC source.