Astaxanthin is one of the most potent antioxidant agents with a carotenoid chemical structure present in nature. This compound is common in some marine organisms and is abundantly present in Haematococcus pluvialis microalgae. Astaxanthin may exist in its “free” form or as part of esters derived from fatty acids and protein-derived complexes. There are studies that demonstrate the differences between the biological properties of astaxanthin and some of its derivatives. Astaxanthin may be relatively unstable or difficult to assimilate due to the intrinsic reactivity of the compound. Therefore, several studies have shown methods to obtain and evaluate astaxanthin formulations. This article describes studies that show the antioxidant properties of astaxanthin and some of its esters, both in vitro and in vivo. In addition, the article discusses some formulations based on emulsions and encapsulated micro- and nanoscale astaxanthins and the antioxidant properties of such formulations.