This dissertation advances our understanding of the cross-linguistic variation in the expression of temporal adverbial relations, the semantic polyfunctionality of temporal clause-linking devices, and the areality of temporal clauses in a variety sample of two hundred eighteen languages. The sample of the present study is based on the Genus-Macroarea method proposed by Miestamo (2005), in which the primary genetic stratification is made at the genus level, and the primary areal stratification at the level of macro-areas. I focus on five types of temporal adverbial clauses: (1) when-clauses, (2) while-clauses, (3) after-clauses, (4) before-clauses, and (5) until-clauses.With respect to the expression of temporal adverbial relations, it has been claimed that they tend to be signaled by free adverbial subordinators, such as English ‘after’, ‘before’, ‘until’, ‘since’ (Harder 1996; Kortmann 1997). However, I demonstrate that languages may also resort to other formal means, such as ‘and then’ coordinating devices, verb-doubling constructions, and correlative constructions. Furthermore, I show that in many languages of the world, temporal clause-linking strategies may make use of open class categories, such as temporal nouns used as clause-linking devices and verbs used as clause-linking devices. These temporal clause-linking strategies may be characterized as devices not (yet) fully grammaticalized. Regarding the semantic polyfunctionality of clause-linking devices, most studies that have addressed this domain have only taken into account a particular type of device (e.g. Kortmann 1997) or two types of devices (e.g. Hetterle 2015). Accordingly, it is not clear whether other devices that have been traditionally disregarded (e.g. ‘and then’ devices) will show polyfunctionality patterns not attested before. The semantic polyfunctionality patterns attested in the present study align for the most part with those documented by Kortmann (1997) and Hetterle (2015). However, I show that there are polyfunctionality patterns not addressed in their studies (e.g. the overlap between ‘while’ and ‘without’) that can inform theories of clause-combining and semantic change. I demonstrate that these rare patterns can be explained by various conceptual factors. As for the areality of temporal clauses, it has been proposed that rare linguistic patterns have high genetic stability and strong resistance to areal influence (Nichols 1992: 181). However, I show that even rare linguistic patterns may be diffused through language contact. Many temporal clause-linking devices that are cross-linguistically rare occur in areal clusters, suggesting that language contact has played an important role in their cross-linguistic distribution. In this dissertation, I develop a series of methodological steps for determining the directionality of spread of rare temporal clause-linking devices.