What are the guidelines for proficiency in the English language for an international applicant?

Adequate command of spoken and written English is essential to success in graduate study at Harvard. Applicants who are non-native English speakers and who received their undergraduate degree from an academic institution where English is not the primary language of instruction must prove their English proficiency by earning either a minimum score of 80 on the Internet based test (iBT) of the Test of English as a Foreign Language (TOEFL) or a minimum score of 6.5 on the International English Language Testing System (IELTS) Academic test.”