This article is a study in the use of irrealis in complementation in the two Baltic languages, Lithuanian and Latvian, and in two Fennic languages, Estonian and Finnish. Four domains of complementation are singled out: propositional, desiderative, apprehensional and evaluative. All investigated languages show limited use of irrealis in the propositional domain (in identical conditions, viz. under main clause negation), as well as in the apprehensional and evaluative domains. The most important differences are observed in the state-of-affairs domain, in particular with desiderative predicates, where Lithuanian shows consistent irrealis marking whereas Finnish has mostly realis. Estonian and Latvian are intermediate. Estonian has a rather strong predominance of irrealis, but it might be recent; in Latvian realis and irrealis are about equally distributed, but this situation seems to differ from that in Old Latvian. In these two languages changes seem therefore to have been going on, and areal convergence might to some extent have been involved in this.