Abstract Nanodiamond (ND) has appeared as a subject of tremendous research interest in recent years due to unique structural features and combination of unique properties. The synthesis strategies, chemistry, and structure of ND have been discussed in this chapter. When reinforced into polymers, this carbon nanomaterial may remarkably improve the properties of polymer matrix even at low loading level. Preparation routes for polymer/ND composite (in-situ polymerization, melt mixing, and solution processing) have also been conversed in this regard. Moreover, the essential characteristics such as thermal, mechanical, electrical, and other physical properties of polymer/ND composite are focused. This chapter also covers potentially important polymer/ND hybrids and their applications in number of growing technologies including defense, electronics, and energy storage devices and systems. Toward the end, this chapter elaborates current challenges associated with this exciting class of nanocomposite.