The goal of this study is the analysis and description of the category of reflexivity in Polish and Croatian, with a focus on reflexive verbs. Although Polish and Croatian are genealogically close and typologically similar languages, the category of reflexivity has been described differently in extant literature on the subject in these languages. For example, Polish authors often relate reflexivity to the notion of voice (passives, medium), while Croatian studies focus on reflexive verbs as a separate verb category. For Polish, there does not seem to exist a mid-level classification of reflexive verbs, one is often presented in Croatian grammars. It was the diverse nature of extant approaches to reflexivity in Polish and Croatian that motivated us to explore the topic within the boundaries of a doctoral disseration. Furthermore, reflexivity in Slavic languages is a frutiful topic of investigation, as evidenced by numerous studies of reflexivity in East, West and South Slavic languages. However, it came to our attention that a contrastive study of reflexivity in Polish and Croatian has not been conducted, as to our knowledge. This insight was our main motivation for this dissertation, as it would expand existing studies on reflexivity in Slavic languages, and hopefully beyond. Goals of our study were twofold. One goal was to present and unify current research on reflexivity in Polish and Croatian and to investigate similarities and differences in the functions of the reflexive marker się / se from a lexical, derivational and syntactic perspective. Another goal of our study was to investigate and categorize groups of reflexive verbs according to their syntactic, morphological and semantic properties, and compare them in a contrastive analysis theoretical and methodological framework. In our study we point out that contrastive analysis has a long tradition in Slavic philology and linguistics, and advocate integrating corpus-based methods in current contrastive research. Reflexive verbs for this study were taken from a dictionary of Polish Uniwersalny słownik języka polskiego (USJP 2003), and contexts in which they are used were attested in general corpora of Polish and Croatian, Narodowy korpus języka polskiego (NKJP), Croatian National Corpus and hrWaC (Croatian Web Corpus). A representative sample of various reflexive verbs from the aforementioned lexicographic resource was complimented with usage data from corpora, providing insight into contextual similarities and differences of reflexive verbs in the two languages. 470 reflexive verbs in Polish were investigated along with their Croatian translational counterparts. It was shown that the reflexive marker has several functions in Polish and Croatian: it expresses semantic reflexivity, introduces changes to the argument structure of the verb, plays a role in lexicalization and derivation of new verb forms and expresses other semantic categories in close relation to reflexivity, such as reciprocity. In order to break down these various functions we introduced a series of syntactic and semantic tests which serve as the basis for our classification of reflexive verbs. These were used as a tertium comparationis of our contrastive analysis. Based on the tests we identified the following groups of reflexive verbs in both languages: reflexiva tantum, reciprocal verbs, true reflexives (semantically reflexive verbs), false reflexives 1, false reflexives 2 and reflexive redundant verbs. Reflexiva tantum is a group of verbs which only have reflexive forms. With regards to this property, we approached the analysis from a standpoint of derivation. We divided the group into prefixed and non-prefixed verbs, as well as those with the same or different lexical root in Polish and Croatian. The analysis shows that within each subgroup there are differences in derivational patterns in which the reflexive marker has a derivational role and can be understood as a morpheme-satellite. Prefix + reflexive marker can be seen as a circumfix. Reciprocal verbs are a group in which context plays a key role since many verbs can have both reciprocal and reflexive interpretations based on different contextual constraints. However, some verbs can be seen as intrinsically reciprocal based on their lexical semantics. In this group we examined other means by which reciprocity can be expressed in Polish and Croatian. One interesting difference is the use of the syntagma Pol. z(e) soba ‘each other; lit. with oneself’, which in Croatian has the meaning of reflexivity proper, opposite to Polish. True reflexives are verbs that have the reflexive marker as a direct object and the marker is closest to its original pronoun status. The complex status of the reflexive marker points to the importance of the semantic level of analysis, where on the level of the argument structure the arguments of Agent and Patient are co-referent. False reflexives, usually regarded as one large group of reflexive verbs, were split into two subgroups, which is an innovation of our classification. In false reflexives 1, the reflexive marker does not introduce substantial semantic shifts in the meaning of the verb lexeme, but changes its syntactic frame. This group is most closely related to passives and impersonal constructions formed with the reflexive marker, which is further supported by the fact that they mostly belong to state or change of state verbs. False reflexives 2 show a rather different role of the reflexive marker, where the addition of the reflexive markers creates a new meaning of the verb and thus plays a role in the lexicalization of polysemous verb senses. The last group, reflexive redundant verbs, is defined by the fact that the addition of the reflexive marker introduced no changes in the syntactic and semantic properties of the verb and can thus be regarded as a stylistic and facultative element. Interestingly, both languages show the existence of such a group of verbs, pointing to the fact that reflexive markers play a broader role in discourse. We hope that this study contributes to extant contrastive research of Polish and Croatian, especially research that deals with phenomena on the borderline between lexical and grammatical categories. We also hope that the present classification of reflexive verbs will find its application in teaching Polish as a second language in a Croatian setting (and vice-versa).