Mohammad Hossein Shahrmiany

Since seventy percent of the earth’s population is thought to be bilingual or multilingual (Trask,1999).It is believed that bilingualism is the norm for the majority of people in the world.Iran is a multilingual country with linguistic and cultural diversity. Minority languages such as Turkish, Kurdish, Baluchi and Arabic are spoken in Iran. Iranian community is dominantly a bilingual community. Persian (Farsi) as an official language used as linguistic and cultural homogenization.With regard to the advantages and disadvantages of bilingualism or multilingualism different views have been expressed by researchers in the field as follows:1-Some research studies in the 1970s and 198s demonstrated that bilingualism positively influences the child’s cognitive and social development.(Fleming &shen,1971).2-Bilingualism has a positive effect on foreign language achievement.(Lerea & Laporta)3-Comparing the performance of Bilingual EFL students with monolingual EFL students on vocabulary knowledge test and word reading skill test4-Bilinguality is highly correlated with breath of vocabulary knowledge and reading skill.