Selenium (Se) stands out as an essential trace element in nature, vital for various organisms, including humans, animals, microorganisms, while being beneficial in plants. Selenium deficiency in diet poses a global problem, with severity often depending on selenium concentrations in the soil. Selenium plays a crucial role in antioxidant processes and regulates reproductive and immune system functions in human health. In response to this challenge, biofortification becomes a key strategy for increasing selenium content in plants. Meta-analysis suggests that foliar application of selenium in the form of selenates often yields better results than soil application, except for rice, where selenite proves more effective. Field studies in Bosnia and Herzegovina, Serbia, and Croatia provided data on selenium availability in soil, using soil samples for chemical analysis to explore connections between chemical properties and selenium presence in the soil's water phase. Based on these data, a Partial Least Squares (PLS) regression model was developed, offering guidelines for planning biofortification in key agricultural production. Physiological parameters (ascorbic acid, total phenols, proline, total antioxidant activity, and lipid peroxidation) were examined in response to osmotic stress induced by polyethylene glycol (PEG treatment) in germinating soybeans (Glycine max L. Merr.), whose seeds were biofortified with selenium in the previous season, investigating differences in reactions of two soybean cultivars (Sonja and Lucija). Furthermore, the impacts of different growth substrates, including peat, vermicompost, and their mixtures, on the efficiency and yield of selenium biofortification in lamb’s lettuce (Valerianella locusta L.), were studied, emphasizing peat reserve preservation. Finally, a comparative study explored the influence of biofortification with sodium selenate (Na2SeO4) and selenium nanoparticles on various "baby leaf" vegetables (lamb’s lettuce and amaranth – Amaranthus caudatus L.) in a hydroponic system, examining potential benefits and differences between these approaches through morphological and physiological features of "baby leaf" vegetables.