Can I upload a Book to Arxiv which I have already Published? A few years ago I published a book on mathematics and physics.  This book received positive feedback from people who read it, but was never widely read and has not sold that many copies.  At this point, I would prefer if the book were just made freely available as it is probably never going to make a huge amount of money anyway, so I was wondering if I could make some alterations to the manuscript and then upload it to Arxiv with a summary of the content and the intended reader?

Would this be copyright infringement as I suppose I have already signed a contract with the publisher?  I don't remember the details of the contract, but I suppose the publisher would not want me to do this, as it means people who might happen to want to read it will do a Google search and see that there is a free PDF copy, whereas the publisher would want to make money from the book wherever possible.  Is there something about Arxiv which sidesteps this copyright issue, as I am uploading a slightly different document to Arxiv which will exist independently of the physical book.
It's very dangerous to say "I suppose I have already signed a contract". This is legal stuff. The exact wording is important! If you have signed a contract, take it out and read it. What exactly did you agree to?

The odds are good you'll have to ask the publisher about whether you can do this. Even if the contract said you can't do this, it's possible they'll still say yes, especially if they've stopped actively trying to sell the book. Nonetheless, they might impose other restrictions - for example they might say you can only post the raw manuscript (i.e. no redrawn figures, no title &amp; half-title pages if they were prepared by the publisher, no book cover [again if it was prepared by the publisher], no special fonts ...).

In any case asking the publisher is never going to be wrong, so I recommend doing that.