Here is a snippet from the homepage:
Codex Sinaiticus is one of the most important books in the world. Handwritten well over 1600 years ago, the manuscript contains the Christian Bible in Greek, including the oldest complete copy of the New Testament. Its heavily corrected text is of outstanding importance for the history of the Bible and the manuscript – the oldest substantial book to survive Antiquity – is of supreme importance for the history of the book.
It is really a fantastic site and gives you much important information (in addition to the digitized photographs of the codex itself).