Initially it seemed like a good idea to revise this book, because so much has been learned about star and planet formation over the last ten years. It eventually became clear that it was a bad idea to revise this book, because so much has been learned about star and planet formation over the last ten years. By then I was halfway through and it was too late to back out.

I therefore beg the reader's indulgence for things I have left out or treated schematically. At some point in a project like this “the best is the enemy of the good”, as Voltaire apparently said; just give up and send it off. Perhaps there is some value in having a treatment that does not try to cover everything in an enormous tome, but instead provides accessible points of departure. As was the case for the first version, I hope that this will be a useful reference for non-specialists as well as a starting point for researchers entering the field.