The writing of textbooks and making them freely available on the web is an idea whose time has arrived. Most college mathematics textbooks attempt to be all things to all people and, as a result, are much too big and expensive. This perhaps made some sense when these books were rather expensive to produce and distribute–but this time has passed.

A few years ago when I first posted a list of mathematics textbooks freely available on line, there existed only a handful of such books. Now there are many.