Carbon dots (CDs, sp² hybrid carbon dots) and nanodiamonds (NDs, sp³ hybrid carbon dots) as new types of biocompatible carbon-based nanomaterials have attracted tremendous attention because of their low toxicity, excellent water solubility, ease of synthesis and functionalization, and outstanding photostability. In this chapter, we introduce the fabrication and fundamental properties of CDs/NDs and then focus on their recent bioapplications in bioimaging. In addition, remaining challenges and perspectives for future developments are also briefly discussed. We hope this chapter will provide critical insights to inspire further exciting research on CDs/NDs for biological imaging applications, to better realize the potential of these intriguing nanomaterials.