The thesis presents a study of the nontrivial interface of morphology, phonology and semantics found in the distribution of three Russian aspectual prefixes O, OB and OBO. These prefixes can be semantically identical when occur in the forms of the same paradigm (e.g. obo-drat’.INF. vs. ob-deru.1 PERSON.SG.FUT. ‘flay’), but can also carry strikingly different meanings that even yield minimal pairs (e.g. o-sudit’ ‘condemn’ vs. ob-sudit’ ‘discuss’). There are some phonological restrictions on their use but they tolerate a lot of variation in the choice of the prefix. Thus, the behavior of O, OB and OBO does not completely satisfy either of the two crucial criteria of regular allomorphy: first, their distribution is not precisely complementary; secondly, their semantics can be both identical and strikingly different.