This article provides an overview of various nanoparticles (NPs) widely used in fluorescent bioimaging, particularly for imaging cells and tissues. It begins with an introduction and a discussion of the advantages of fluorescent NPs over molecular fluorophores, labels, and probes. The article then assesses the types and specific features of nanomaterials commonly used in bioimaging, including fluorescently doped silicas, sol-gels, hydrophilic polymers, hydrophobic polymers, semiconducting polymer dots, quantum dots, carbon dots, other carbonaceous materials, upconversion NPs, noble metal NPs, and dendrimers. The article also covers surface modification techniques and methods for coating NPs. Specific examples of NP applications in plain fluorescence imaging, targeted imaging, imaging of chemical species, and imaging of temperature are provided. Additionally, the article discusses multimodal imaging, imaging combined with drug and gene delivery, and imaging combined with therapy or diagnosis. The electronic supplementary information (ESI) includes specific examples of materials and methods used in imaging, sensing, multimodal imaging, and theranostics. The article contains 273 references in the main text and 157 references in the ESI.This article provides an overview of various nanoparticles (NPs) widely used in fluorescent bioimaging, particularly for imaging cells and tissues. It begins with an introduction and a discussion of the advantages of fluorescent NPs over molecular fluorophores, labels, and probes. The article then assesses the types and specific features of nanomaterials commonly used in bioimaging, including fluorescently doped silicas, sol-gels, hydrophilic polymers, hydrophobic polymers, semiconducting polymer dots, quantum dots, carbon dots, other carbonaceous materials, upconversion NPs, noble metal NPs, and dendrimers. The article also covers surface modification techniques and methods for coating NPs. Specific examples of NP applications in plain fluorescence imaging, targeted imaging, imaging of chemical species, and imaging of temperature are provided. Additionally, the article discusses multimodal imaging, imaging combined with drug and gene delivery, and imaging combined with therapy or diagnosis. The electronic supplementary information (ESI) includes specific examples of materials and methods used in imaging, sensing, multimodal imaging, and theranostics. The article contains 273 references in the main text and 157 references in the ESI.