Selenium is one of the most important trace elements in animal nutrition, as it helps animals stay healthy and productive. Selenium is a vital component of poultry nutrition, and its bioefficacy is determined by the chemical form in which it is consumed. Inorganic Se, such as sodium selenite, and organic Se, such as Se-enriched yeast, DL-selenomethionine, and nano-selenium are available as Se supplements in the poultry diet. Because chickens are unable to synthesize Se, dietary supplementation is an important technique for combating commercially significant stressors. Indeed, in stressful situations, when increased selenoprotein expression necessitates additional Se, and Se provision via feed is typically reduced due to reduced feed consumption, Se reserves primarily in the muscles could help maintain an effective antioxidant and prevent stress-related harm. For commercial application, the poultry industry is looking for the most effective sources of environmentally friendly Se. The benefits and drawbacks of Se sources for poultry (inorganic, organic, and nanoparticles) are discussed in this review, as well as future directions for the development of new Se sources and the recommended levels as well as the mode of action.