This Ph.D thesis compares different dialects, including the Celtic varieties Scottish and Irish English, with regard to mainly adnominal relative clauses. Other types of relative clauses (nominal relative clauses, sentential relative clauses, and intermediate types assembled on a cline) are treated in brief. The approach is partly descriptive, partly functional, over which a typological grid is placed. Based on data primarily from FRED Corpus, which has been compiled at the University of Freiburg, relative clauses are categorized and commented on, as well as counted and documented in tables and charts. An exhaustive overview of adnominal relative clauses in different regions is given without making any attempt at drawing another dialect map. Apart from the degree of subordination of relative clauses, the structural means employed in relative clause formation are centered on. Dialectal variants of relative particles and nonstandard usages of relative markers are brought into focus. Particular emphasis will be put on resumptive pronouns, nonreduction, and copies. Determining factors for the occurrence or nonoccurrence of these structural means are looked for and correlations established between the cline of subordination and the cline of explicitness of structural means. Cognitive hierarchies and theories, such as Keenan & Comrie's (1977, 1979) Accessibility Hierarchy, Bever & Langendoen's (1971, 1972) account on the perceptual difficulty of zero subject relative clauses, and the interrelationship between position of relative clause (medial, final, extraposed) and mental processability, are checked against the data.