This paper examines the major phonetic and phonological differences between British and American English. Although both varieties share the same linguistic foundation, they differ noticeably in pronunciation, vowel quality, consonant realization, and stress patterns. The study focuses primarily on Received Pronunciation (RP) as a representative model of British English and General American (GA) as the standard form of American English. Key aspects such as rhoticity, vowel variation, consonant processes including flapping and glottalization, and differences in stress and intonation are analyzed. The paper also discusses historical and social factors that contributed to the divergence of these two varieties. The findings suggest that phonetic and phonological variation plays an important role in language learning, accent perception, and intercultural communication. Understanding these differences can help learners, teachers, and linguists develop greater awareness of spoken English in global contexts.