This dissertation is a comparative study of the class of verbs commonly termed "reflexive" in Russian and Bosnian/Croatian/Serbian (BCS). These verbs occur with the affix -sja in Russian and with the clitic se in BCS. Despite the fact that they are commonly called reflexive, they do not necessarily refer to reflexive events in which the same entity is both agent and patient.. The analysis has an emphasis on semantics and uses Cognitive Grammar as a framework to determine the semantic prototypes for this group of verbs in each language. It uses as a starting point Suzanne Kemmer's (1993) monograph on middle voice, which shows that Russian is a middle-marking language in which the light form -sja denotes middle voice and the heavy form sebja denotes true reflexivity. The study hypothesizes that Kemmer's analysis is accurate for Russian, but not for some other Slavic languages, namely BCS. Quantitative and qualitative analysis shows that in Russian the semantic prototype for verbs with -sja is MIDDLE, while in BCS the prototype for verbs with se is REFLEXIVE. The study defines semantic types for this group of verbs including REFLEXIVE, POSSESSIVE REFLEXIVE, RECIPROCAL, IMPERSONAL, PASSIVE, MIDDLE and BENEFACTIVE and sets up diagnostic tests for determining REFLEXIVE, POSSESSIVE REFLEXIVE, and RECIPROCAL events. Quantitative analysis is based on data collected from the Parasol parallel corpus from three parallel texts and shows that both languages have MIDDLE as the most frequent semantic type for SE-verbs for both languages, but also that that Russian sometimes uses a heavy form for REFLEXIVE, POSSESSIVE REFLEXIVE, or RECIPROCAL semantic types where BCS has a light form SE-verb. Qualitative data shows that BCS SE-verbs occur in various situations unique to BCS and not in Russian, including across-the-board dependencies, past passive participles formed from SE-verbs, and se modified by adjectives as a noun or pronoun would be modified. The combined quantitative and qualitative analysis shows that BCS SE-verbs maintain the syntactic structure of REFLEXIVE verbs, pointing to the conclusion that the prototype for BCS SE-verbs is REFLEXIVE, while the prototype for these verbs in Russian is MIDDLE.