We investigate the causal effect of English proficiency on labour, social and health outcomes of immigrants in Australia. We use age at arrival combined with country of origin to form an instrument of English proficiency. We find that immigrants in Australia with better language proficiency are able to earn higher income, attain higher level of education, have higher probability of complete tertiary studies, and get more hours of work per week. Language proficiency also improves social integration, leading to higher probability of marriage to a native and higher probability of obtaining citizenship. We find only limited evidence with respect to the hypothesised causal relationship between language and health for immigrants. This last result may be due to small sample sizes.