Selenium, primarily a chalcogen group non-metal, sometime referred to as a ‘metalloid’ has several allotropic modifications, six stable natural isotopes (74Se (0.9%), 76Se (9.4%), 77Se (7.6%), 78Se (23.8), 80Se (49.6%), and 82Se (8.7%)) and occurs in a range of oxidation states, viz., −1, 0, +2, +6. There is an upsurge in research on synthesis of nanomaterials, their technological leverage and diverse applications in energy, nutrition, environment and health sectors. Recent works have established the potential role of selenium-based nanoparticles in agricultural fields and food industry as packaging materials. The element has been recognized to be an essential trace element for animal but not for plants. Selenium nanomaterials, selenium nanoparticles (SeNPs), in particular have drawn a lot of attention currently for their potential applications originating from their role as antioxidants, antimicrobials, and anticancer agents. Selenium nanoparticle’s bioavailability compared to bulk selenium render such nanosystems promising candidates for drug delivery in controlling diseases. The role of Se and its nanocomposites in relation to plant physiology and toxic substance remediation have assumed remarkable significance over the last decade to be specific. These developments has spurred intense research worldwide on the fabrication of selenium nanoparticles and its composite materials. Various strategies have been adopted including utilization of biological resources green approaches for accessing Se-based nanomaterials. The present review deals with synthesis, characterization and applications of selenium-based nanoparticles covering a period of preceding 12 years highlighting the nanocomposites.