The process in which a microorganism (or other particulate material) is rendered more susceptible to phagocytosis by coating with an opsonin, a blood serum protein such as a complement component or antibody. [ GOC:add https://www.worldcat.org/search?q=bn%3A0781735149 GOC:mah https://www.worldcat.org/search?q=bn%3A068340007X https://www.worldcat.org/search?q=bn%3A0198506732 ]