This chapter aims to collect and summarize the chemical properties of cobalt and some new cobalt compounds. It deals with the progress of cobalt chemistry. Cobalt has been substantial in both chemical reactions and within many compounds. Some of them are heterocyclic reactions, cobalt-based catalyst and cobalamin. Also, it discusses variety of applications of cobalt in a wide range of areas and toxicity of cobalt. The studies carried out in this area so far have enabled and will be continued to be responsible for producing unknown and difficult reactions. This survey of the recent literature illustrates the fact that many different approaches on cobalt and new cobalt compounds are being used in many different areas.