We describe the development and use of an online textbook for first-year calculus, the second edition of a book that first appeared in print. The principles on which the book is based are the same as those the first two authors developed in Project CALC more than a decade ago, but the online version has many interactive features that could not be in a print-based text. We expect the book to be published by the Mathematical Association of America, but for the time being (while development continues), it is freely available to all at http://www.math.duke.edu/education/calculustext. We are eager to have teachers and students use any or all of it and provide feedback.