Miscellaneous reductants are of focus for their role in colloidal synthesis/preparation of metal nanoparticles. Their reductivity from weak to medium is first demonstrated with selective effect to noble and less reactive transition metals with respect to different synthesis conditions. After this, we discuss the origin of the reductant property. Besides, other important and delicate functions of these reductants in the synthesis will be reviewed including the stabilizing effect and the size- and shape-controlling capability. It is also important to emphasize that reductants in this chapter compose a group of much greener and less toxic reagents for the nanoparticle synthesis.