When I want to find out more about a what a particular book is about, or browse through books on a specific topic, the first resource that comes to mind which helps me do all this is Amazon.
Amazon is an American-based, international online retailer. While they today offer customers a wide range of products to purchase at discounted prices through their website, they started off with, and was led to fame with selling books.
In addition to being an online bookstore, they enabled customers to participate in writing book reviews and ratings, and posted these alongside professional editorial book reviews. While customer product reviews may be seen as the norm today with other websites that advertise and sell products, it was a novel idea at the time when there was nothing like this around. Amazon may inarguably be one of the first, if not the first to do this. As a result of this long-standing service, and the large customer base, Amazon has become the go-to resource for book reviews.
