One of my Regency hobby-horses is the use of titles.  I’m afraid it makes me crazy if an author spends the time to write a novel set in our era and neglects the proper titles for her aristocratic characters.  Indeed, an author who’s writing I love has been known to make me wild by getting titles wrong book after book.  Come on, honey.  You should have figured this out by now.
I have had this rant before on other sites, so I will not take too much space with the ranting and, rather, devote this post with some advice about how to get it right.  It’s not that difficult.

Let’s start out with what not to do:  A duke is never my lord or your lordship.  He’s not Lord anything.  Most frequently a title is not the same as a last name and they are never interchangeable.  Earls, marquesses, and viscounts are never Lord Surname and certainly never Lord Given Name.  Dukes, as we have established, are never Lord anything.  Last names and titles, if different, are not interchangeable when addressing an aristocrat.  There’s only one right way to do it.

Now, on to that right way.
A duke is “your grace” or “his grace.”  The same goes for his duchess.  His title is “Duke of Title.” For example, Peregrine Cavendish is the Duke of Devonshire.  He is never Lord Devonshire or Lord Cavendish.  His peers may call him Duke rather than Your Grace.
An earl is Lord Title, never Lord Surname or Lord Given Name.  For example, John Montague is the Earl of Sandwich and is addressed at Lord Sandwich..  Friends might refer to him as Sandwich.  His wife is the Countess of Sandwich and is called Lady Sandwich.  In a few cases, such as Earl Spencer, the title and surname are identical.
A Viscount is also Lord Title.  Edward Pellew is Viscount Exmouth and would be addressed as Lord Exmouth.  His wife is Lady Exmouth.

Barons are also referred to as Lord Title.  Barons, more frequently than other titles, may have titles that are the same as their surname.  For example, William Hawke is Baron Hawke and is called Lord Hawke. His wife is Lady Hawke (and may or may not be played by Michelle Pfeiffer). This is not always the case, however, and you should be sure that, whichever you choose, your title remains consistent.

So these are the basics.  It goes on from there.  Oldest sons of dukes, marquesses and earls usually take one of their father’s lesser titles as a courtesy title (if one is available) and would, thus, be Marquess, Earl, or Viscount of Whatever.
Younger sons of dukes and marquesses have the courtesy title of Lord, but they use their first names.  Lord Peter Wimsey is Lord Peter, never Lord Wimsey or Lord Denver (his older brother is the Duke of Denver).  And, moreover, his wife would be Lady Peter.  Cool, huh?
Younger sons of earls, viscounts, and barons are just “honorable” and are usually addressed as “Mr.”
Daughters of peers are Lady Given Name regardless of their birth order.  In Pride and Prejudice, Lady Anne Darcy and Lady Catherine deBourgh are the daughters of an Earl (which one, we’ll never know).  This applies to daughters of dukes, marquesses, and earls.  It does not, however, apply to the daughters of viscounts and barons.  Like the sons, they are just honorables and addressed as “Miss.”
Have written these down, I realize they don’t look as easy as I may have lead you to believe.  However, I have a couple of web sites for you that will make it much easier.
Laura Wallace created and maintains the fantastically useful British Titles of Nobilitywhich takes on all this stuff and more in an easy-to-understand layout.  If you bookmark this site, you need never wonder if you’re using the right title.  For something not as detailed or exhaustive (just the basics, ma’am), I give you the table of honorifics from the Jane Austen Information Page at The Republic of Pemberley.
So, there it is.  Yes, it’s a little convoluted but if you love your subject and your era, and you’re going to write about it, it’s not too much to ask that you get the details that are easily available to you. Right?  If you don’t know it, look it up.  Or ask a friend who does.
Here’s the final question.  Am I alone in being driven wild by misuse of titles?  Does this make you tear your hair out or are you able to overlook it and get on with the story?