When M.A.S. Abdel Haleem was a youngster in Egypt all the boys in his school were required to memorize the entire Quran and were tested annually to make sure they maintained this knowledge.

The veteran University of London professor of Islamic studies says he obeys a promise to his father to read the Quran daily, and the childhood training means he doesn't need a printed text. "I can do this anytime, even when I am walking or riding the Underground."

Haleem has put his lifelong immersion in the Quran and the Arabic language to good use the past seven years, working on a new Quran translation in English that appeared last month: "The Quran" (Oxford University Press).

It's hard to overstate the importance of the Quran, which defines the belief and conduct of a billion-plus Muslims, including a growing number of immigrants in English-speaking nations.

Unlike Christians with their Bibles, Muslims believe the Quran is scripture only in Arabic because it existed in that form in heaven before it was revealed to the prophet Muhammad. Only the Arabic is literally God's word and is always used in Quran quotations during rituals and sermons.

In times past, there were debates about whether it was even proper to translate the scriptures. Early English versions came from non-Muslims (the subtitle of the very first, in 1649, called the Quran "the Turkish vanities"). No Muslim produced an English Quran till the 20th century. But nowadays even strict Muslims promote English editions to aid "dawah," Arabic for "call," meaning missionary work.

Haleem says translations are essential so that Muslims in the West, including his own children and grandchildren, can remain knowledgeable. Georgetown University's Yvonne Haddad says most immigrants' children "cannot read the Quran in Arabic. They may recite it, but they don't understand it."

As with the Bible, there are numerous English Qurans on the market, though experts say many have limitations.

While most English Qurans retain old-fashioned, King James-style English, Haleem employs 21st century language. A reviewer for Britain's The Economist said he transformed the Arabic "into a form of modern English which reads easily and flows smoothly without taking liberties with the inviolable text."

The most widely distributed English Quran — thanks to Saudi Arabian sponsorship — is probably the 1934 edition by India's Abdullah Yusuf Ali, as revised in 1989 at the International Institute of Islamic Thought in Herndon, Va. Yusuf Ali's terminology is notably fusty, for instance in this passage about the day of judgment: