As soon as the author pens down the book, he owns the copyright over his work. However, there is always a need of written registration. Copyrighting a book is imperative today. With book stores mushrooming all over the place and online stores taking over the market, copyright over a book prevents the stores, both online and physical, from buying a copy and publishing it copies. For different books there are different copyright guidelines, for a book solely based on facts, copyright follows a narrow spectrum whereas for something like a novel, it extends to a wider frame and covers almost everything that is there in the book. However, if you know about how to copyright a book you will find out that copyright registration is not that difficult of a task.
Copyright prevents copying but it does not guarantee any law using which you can stop simultaneous creation of the work done by you. So to avoid this predicament, an author should always strive for registering his work as soon as he incepts the idea and sets his foot on it. Once the book is registered it is basically a prior intimation to the world that this is your work and one will require your consent to republish it in parts or wholly. On the other hand, having failed to register a book, an author might have to struggle later to prove that the plagiarised book has been his creation and the person who has plagiarised his work accessed it before it could be published.