The chapter introduces magnetotactic bacteria and discusses its occurrence in the nature and methods applied for studying them. The structure and the physiology of the bacteria is also discussesd. The processes of magnetite biomineralization in magnetotactic bacteria are reviewed. The structural, morphological, and crystal growth properties of the magnetite inclusions are described and proposed mechanisms of biomineralization are discussed. Magnetotatic bacteria exhibit magnetotaxis as a consequence of magnetite inclusions in their cells. Palaeomagnetism is a marked phylogenetic diversity within this group of organisms. These organisms provide clues about geochemical changes in the earth's atmosphere. Although there are several magnetic minerals, the most observed and magnetically stable phase in these sediments is magnetite. The chapter also discusses its biotechnological applications. There are many commercial uses of the minute permanent magnets of magnetotactic bacteria, such as in the manufacture of magnetic tape and magnetic printing inks.