The thesis analyses a variety of clause linkers used in the world’s languages as dedicated markers of four circumstantial relations between states of affairs: anteriority (‘after’), causality (‘because’), purpose (‘in order to’) and conditionality (‘if’). Focusing primarily on the function of the linkers rather than on their formal properties the study scrutinizes the origin and functioning of free-word adverbial subordinators, converbal endings as well as other subordinating affixes and polymorphemic structures specialized for clause-linking functions. The database consist of nearly 700 items which come from a geographically and genetically balanced sample of 84 languages. In the first part of the thesis I discuss in detail the scope of the study, theoretical foundations (functional approach to language analysis) and methodology. In the second part I focus on the issues of grammaticalization and semantic scope of the linkers. The analysis of patterns of polysemy of the linkers, as well as the make-up of the polymorphemic items among them provide material for the reconstruction of the most common sources and pathways of grammaticalization. Looking closer at the patterns of semantic polyfunctionality (i.e. other circumstantial meanings that the clause linkers convey in addition to being markers of the four analysed relations) I reveal the architecture of the network of their cognitive affinities. The result of this investigation is a set of findings, which add to our understanding of the origin and functioning of the markers – a topic which has received little attention so far. The third part of the dissertation is dedicated to the analysis of the crosslinguistic variation in the degree of grammaticalization, lexicalization and explicitness of the linkers and discussion on the motivations behind their development. The main body of the analyses is focused on the investigation of the potential influence of a variety of socio-cultural factors on the variations observed. The factors include those most often mentioned in the context of the forces shaping language structure: presence and vitality of written form as well as other media of displaced communication, presence of the language in schooling, population size of the speech community, and type of society. The results obtained show that the degrees of grammaticalization, lexicalization and explicitness are much stronger correlated with socio-cultural factors for anteriority and conditionality than for causality and purpose. In order to account for the differences I evoke the concepts of cognitive salience and communicative pressure arguing that the influence of socio-cultural factors on language structure should always be considered in a broader context which includes also pragmatics and cognitive psychology.