In U.S. law, book titles cannot be copyrighted. That means that in most cases, there is nothing to stop you from publishing a book that has the exact title of a book that is already published. Equally, there's usually no way you can stop someone from publishing a book that has the very same title as one that you wrote.
The big exception is where someone has registered a trademark for a book series or a key component of a book series. For example, "For Dummies" is a federally registered trademark, as is "Harry Potter." If they have not registered a trademark, they can't stop you from crowding in on their title. I once had a conversation with Jay Conrad Levinson, the author of the phenomenally successful Guerrilla Marketing series of books, in which he regretted not having trademarked the phrase, Guerrilla whatever. Because he hadn't done so, he was unable to stop other authors from using the phrase in their book titles, such as Guerrilla PR or Guerrilla Music Marketing, both of which were unconnected with Levinson.
The small exception is where a book title or character has become sufficiently famous that it's identified with a particular author in the minds of the public, and anyone attempting to publish their own book using the title or character might be guilty of misleading the public and unfairly trading off the other author's reputation and hard work.
Another small exception is for works that are parodies. You won't get into trouble for publishing a humor book lampooning the popular fiction series 50 Shades of Grey with your book 50 Shames of Earl Grey or 50 Shades of Beige.
Additionally, trademark or no trademark, it is always OK for you to be writing a book about another book, such as Reading Harry Potter: Critical Essays or 50 Shades of Grey: A Cultural Analysis (I made that one up).
If these general guidelines don't address your questions, or if you can't keep straight the differences between copyrights and trademarks, then I strongly suggest you set up a consultation with an intellectual property attorney. When it comes to the law, getting informed is the best policy.
In the next lesson, I offer some commentary on the book title I brought up in the course introduction.