Copyright Registration and Library of Congress Registration
You own the copyright to your work the moment you create it. You do not need to publish it, include special "magic" captions in your book, or register your copyright. However, there are definite advantages in terms of enforcing your copyright if you do include a notice in your book and do register your copyright.
The traditional way to give notice that your book is copyrighted is to include a caption on the copyright page, on the back of the title page of your book. It should at least have:
© year copyright owner
for example, © 2005 John Smith
You may also want to include a whole paragraph of things that are not allowed, such as copying, making into a movie, distributing in electronic form, etc. Here are some examples:
All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means whatsoever without express written permission from the author, except in the case of brief quotations embodied in critical articles and reviews. Please refer all pertinent questions to the publisher.
All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by an information storage and retrieval system - except by a reviewer who may quote brief passages in a review to be printed in a magazine or newspaper - without permission in writing from the publisher.
If you register your copyrighted material with the Copyright Office, then you are giving official public notice of your ownership. This helps if you need to take action to enforce your copyright. To get more information on the Copyright Registration and how to pay the $45 fee, see the Copyright Office FAQ's.
All works under copyright protection that are published in the United States are subject to the mandatory deposit provision of the copyright law.
This law requires that two copies of the best edition of every copyrightable work published in the United States be sent to the Copyright Office within 3 months of publication.
The law also requires that the deposit be made automatically. This means that you will not get a reminder to deposit your books.
Mandatory Deposit with The Library of Congress
There is a legal requirement that you deposit 2 copies of your published work within 3 months of publication. This is separate from copyrighting or ISBN matters. For details, see the web site for the Library of Congress here. Copyright registration and mandatory deposit can be handled with a single submission.