Nanodiamonds (NDs) have recently received significant attention as potential drug delivery and diagnostic agents. Several studies have explored new ways to de-agglomerate ND particles, and have also examined their biocompatibility in vitro and in vivo, their ability to load and deliver various therapeutic agents, their role as imaging compounds, and their potential as diagnostic reagents. This broad spectrum of applications is made possible by the versatile properties of NDs, which include scalable processing parameters (e.g., ball milling, acid washing, ultrasonication, etc.), fluorescence properties that are observed with high pressure high temperature (HPHT) NDs that can also be modulated depending on their nitrogen–vacancy center composition, their ability to deliver a variety of drug compounds, and their relative biocompatibility compared to several other potential nanomaterial carriers. This chapter explores the recent developments in the biological and medical applications of NDs and provides a roadmap for their continued development.