Συγκριτική συντακτική ανάλυση του Παρακειμένου της Νέας Ελληνικής και των κυριοτέρων ρωμανικών και γερμανικών γλωσσών. / The present thesis is an analysis concerning the periphrases of the present perfect in Modern Greek, and in the main Romance and Germanic languages, Spanish, Portuguese, French, Italian, English, German and Dutch. It consists of three chapters. In the first chapter, I present the data concerning the formation and the uses of the present perfect in the aforementioned languages. I particularly insist on the fact that in some languages there is auxiliary selection. French, Italian, German and Dutch, on one hand, generally select the auxiliary verb “have” to form the periphrases of the present perfect of transitive verbs, whereas, they select the verb “be” to form the present perfect of unaccusative verbs. Moreover, two of these languages, French and Italian have participle agreement. The participle used in the formations of these periphrases agrees in gender and number with the subject of the phrase if the auxiliary verb “be” is used, whereas, it agrees with the object if the verb “have” is used, but only on condition that the object precedes the participle. This can occur mainly when the object is a pronoun. In the second chapter, I proceed to the syntactic analysis of the data. I look into Kayne’s (1993) analysis on auxiliary selection. Kayne, following Freeze (1992), supports that the syntactic analysis of the possessive “have” should be adopted for the auxiliary “have” as well. He believes that the only difference between the two constructions is the fact that the complement of the auxiliary “have” should be one appropriate for a participle. Moreover, Kayne (1993) supports that the two auxiliary verbs “have” and “be” are basically the same. “Have” is “be” with a locative. In this chapter I also present some additional, more recent views concerning the constructions of the periphrases of the present perfect, the ones of Iatridou (2007) and D’Alessandro (2010). In the third chapter, I look into participle agreement. I suggest that this kind of agreement is related to, and depends on the position of adjectives in each language. In languages like French and Italian the adjective is usually put after the substantive. As a result, participles only agree with the argument they characterize/determine, depending on the construction, if they are in a structural position which is compatible with the position of the adjective. In languages like German and Dutch, adjectives always precede substantives. However, participles never do so when they are part of a periphrasis of the present perfect. German and Dutch never show participle agreement. In Greek, on the other hand, the adjective can either precede or follow the verb. This seems to be the reason why participles in Greek always show agreement. Finally, in English, adjectives and consequently participles never show any kind of agreement due to the fact that they lack clitic morphology. Following Wasow (1977) and his analysis on verbal and adjectival participles, but also Kibort (2005), I support that past participles that show agreement constitute an intermediate participial category between the verbal and the adjectival ones. They seem to be “resultative” participles which act as verbs but bear adjectival features. I propose that it is possible that the function of these participles in the periphrases of the present perfect is either to produce or to reinforce the perfect of result. I conclude that Modern Greek is the only language, among the ones examined, that has unconditional participial agreement, and can produce two different kinds of the present perfect with most verbs, the perfect of experience, on one hand, and the perfect of result, on the other.