The process in which germinal centers form. A germinal center is a specialized microenvironment formed when activated B cells enter lymphoid follicles. Germinal centers are the foci for B cell proliferation and somatic hypermutation. [ http://purl.obolibrary.org/obo/go/references/0000022 GOC:jal http://openisbn.com/search.php?q=081533642X&isbn=1/ ]