Georg A. Feuerstein was an Indologist and, according to his associate Ken Wilber, among the foremost Westerns scholar-practitioners of yoga. After doing his postgraduate research at Durham University in England, he moved to the United States, eventually settling in Canada with his wife and sometime co-author Brenda.
A complete history of yoga stretching back to the dawn of history, and going up to roughly the 18th century or so. This is a pretty academic book, about the philosophical roots of yoga not necessarily the stuff you hear about in a modern yoga class. It is a convoluted and confusing history, and I found the writing fairly confusing as well. At times very dry, at other times a bit corny, such as when the author repeatedly made claims about quantum physics backing up different new agey claims.
For the most part however, as good a guide to the ancient roots of yoga as any.