This book contains St. Isidore's work in the original Latin with an index and doesn't contain a parallel translation (I'm not complaining about this, but some folks familiar with the similar-looking Loeb series might be disappointed).
St. Isidore's "Etymologies" is a landmark work often referred to as a proto-encyclopedia. It was, in its day, a summa of knowledge. For the medievalist, it's a treasure trove of influences and forgotten words of wisdom. Isidore divides the work into twenty "books" (read "chapters") that examine anything from grammar to war. The method of inquiry is ordered and a bit different from what one would expect. While many parts are now inaccurate, it remains a fascinating read that is never dull, and it still contains a good bit of useful and sage information than can be found by the discriminating reader. In a word, non academics can get a kick out of this work as well.
I do have a few complaints, however: the price is outrageous. This is especially true as this work is legally available online in Latin free of cost. The volume (the first of two) here is around 250 pages and is only in Latin. Obviously, St. Isidore isn't getting any royalties and there isn't a translator to skim off the top either. For Oxford to charge almost a hundred dollars for one volume is appalling. The new edition doesn't even have a dust cover! Instead, it's just a cheap hardcover with a plastic laminate. It even looks cheap.
For those without a knowledge of Latin, translations are readily available. Ironically, they're less expensive than the original Latin, despite the cost of a translator. There is an outrageously priced "academic" translation here:The Etymologies of Isidore of Seville which might be a little more useful for research papers, but thankfully there is a reasonably-priced different translation (which is complete!) as well in two volumes here:Isidore of Seville's Etymologies: Complete English Translation, Volume I(vol 1) and here:Isidore of Seville's Etymologies: Complete English Translation, Volume 2(vol 2). The inexpensive edition seems as good as the "Cambridge" translation, so I wouldn't waste any more money than you have to.