Where can I buy English books in Hanoi?
It is quite hard to find a decent English bookstore in Hanoi, since the demand is pretty low and not frequent. The first and only English bookstore in Hanoi until now is Bookworm, which located on 44 Chau Long Street, near Truc Bach Lake. This bookstore trades only English books and magazines, both used and new, with a limitted French collection. There are also many discounted fictions if you want a quick read for your next trip.
Another bookstore, Trang Tien bookstore (44 Trang Tien Str., Hoan Kiem Dist.) also sells many English books, though it is mostly about learning and teaching. The majority of books here are still in Vietnamese.
In order to find English books, you might need to venture out to other book stores around the city. Phuong Nam company has three bookstores in Hanoi: one inside Vincom tower (191 Ba Trieu Str.), one at 20 Ly Thai To Str and one at 87 Lang Ha Str. All of them have foreign sections, with some books, magazines, artbooks and CDs/DVDs in English.
Fahasa bookstore (338 Xa Dan Str, Dong Da Dist) might be worth visiting as well, with around 100 English books of different types. Moreover, Fahasa recently open a new book store at 39 Kim Lien Moi Str., Dong Da Dist, doubling the number of English books, which include some famous classic novels such as Frankenstein, Gone with the wind, Breakfast at Tiffany, The lords of the rings, etc.
In addition, wandering around Dinh Le Str. (the so called book street of Hanoi), you can sometimes find good English books/novels/artbooks at quite low prices. In general, to find a good English book in Hanoi, you must have patience and time but the price is pretty reasonable.