This thesis focuses on regional dialects in the USA and Great Britain. Dialectology is a linguistic discipline that studies varieties of language according to geographical or social distribution. In this paper the essential characteristics of the discipline are highlighted, together with notions of dialect, variety, language, accent, sociolect, idiolect and patois. The main part of the paper consists of the analysis of aforementioned dialects. Maps presented in the paper show us dialect regions according to different criteria; either differences in lexis or those in pronunciation. After analyzing different studies from notable linguists, regional dialects of the USA are divided into three large regions: North, South, and West. Great Britain’s division elaborated in this thesis is mostly concerned with accent differences rather than grammatical or orthographical ones. The main focus in differences between Great Britain and the USA was put on accent, since grammatical ones are not substantial. Vocabulary differences are presented in tables, which are also included in this thesis.