This review is drawn into theoretical, field, and experimental studies in two main areas. The first area involves the investigation of the physical and chemical characteristics of iron (Fe) and manganese (Mn) deposits, and the development of genetic models for use in mineral exploration. The second area deals with the nature of geothermal systems against weathering system as two different sources of the Fe and Mn. It includes inspection of mechanisms of transportation and chemical and biochemical effects during and after the initial deposition and the development of concentrations of Fe and Mn during diagenesis. Available data on physical and chemical properties of recent Fe and Mn deposits are collected and the anticipated diagenetic cycles required for their lithificatoin are discussed on bases of stabilities of iron or manganese minerals or both. To explain the association between diagenesis and Fe and Mn deposits, many examples mostly from unpublished experimental studies carried out by the writer are provided herein.