Limit # of recs on inner join?

I want to limit the number of records returned by an inner join.

Suppose I have a table of Books:

book_id
title

And, a table of authors:

book_id
author_name

Now, suppose I want to get book + author, but I only want one author for 
books with multiple authors.  Traditionally, I'd do something like:

select books.book_id, books.title, authors.author_name
from books
inner join authors on authors.book_id = books.book_id
where books.book_id = ?

This might return:

1    A Cat In The Hat    Dr. Seuss
1    A Cat In The Hat    Dr. Seuss' Partner

Instead, I just want:

1    A Cat In The Hat    Dr. Seuss

How can I limit the inner join?

Cheers,
-J