The present study is concerned with regressive assimilation in Standard English and standard Arabic. A survey of literature is conducted to emphasize on contact, distant, partial, total, manner, voice, and prefix {in-} assimilation in English and optional minor assimilation in Arabic. Thus, a contrastive analysis is investigated to show the similarities and differences between regressive assimilation patterns in English and Arabic. Such analyses have proved that differences are more than similarities since certain sounds in English have no counterparts in Arabic and vise versa. Key Words: phonetics, segments, assimilation, sound, geminated, vowel, articulation, intensity, consonant, regressive, minor, optional, source, target, anticipation, leading, pronunciation, contact, distant, partial, total, manner, voice, prefix, sibilant, feminine, phonological and valorization