In recent years considerable attention has been paid to ferrate (Fe(VI)), +6 oxidation state of iron due to its novel properties such as oxidizing power, selective reactivity, stability as salt, and non-toxic by-products of ferric ion. Especially, much progress has been made on its applications to water treatments as efficient oxidant, coagulant and disinfectant. Reflecting the increasing interests on applications of Fe(VI) as a green chemical, this paper reviewed extensively not only the chemistry of Fe(VI) but also its various applications with focusing on its water treatment applications. The required future works for its widespread and successful applications to various fields were also discussed in the relevant parts.