The physicochemical methods of the synthesis of zinc nanoparticles (ZnO NPs) and some detailed studies on ZnO toxicity mechanism and biokinetics have been reported. However, some of these physical and chemical methods of synthesis are expensive and can also have toxic substances absorbed onto them. Hence, eco-friendly synthesis of nanoparticles due to their easier process, cheaper availability, and high stability is dominating new research. In particular, ZnO NPs which are now being synthesized through major biological systems involved in this are bacteria, fungi, and plant extracts; this has increased studies in various applications in the biological field. In this review, we have elaborated on various natural source-mediated syntheses of ZnO NPs and their role in various biological activities like antimicrobial, anticandidal, larvicidal, cytotoxic, and photocatalytic activities. Apart from these applications, ZnO NPs are also reported to help to prevent dust formation, for several years, on oil paintings. © 2015, Springer-Verlag Berlin Heidelberg.