The United Nations publishes a website called the UN iLibrary which is “the first comprehensive global search, discovery, and viewing source for digital content created by the United Nations.”
It is available to anyone who wants to access information published by the UN, as well as programs sponsored and/or funded by the UN. They plan to add around 500 titles annually and state that around 70% are published in English.
Searching the site is straightforward. You are offered the option of searching by country, topic, country & topic and by simply searching through their catalogue. Most of their publications may be bought in a tangible form in the bookstore. Also you may subscribe to the site for unlimited access, including pdf and browser versions of publications, but the subscription is cost prohibitive at $12,500 per year. Of course that is only practical for large institutions or metropolitan areas in which the site may be used regularly enough to justify such a price tag.