Exactly what Ken said. Look at the documentation for org-latex-classes to see the full description. You can see an example in my Emacs config: https://github.com/zzamboni/dot-emacs/blob/master/init.org#various-exporters (look for the paragraph that starts with "Some customizations for the LaTeX exporter"). Once that is defined, you can specify the name you used as the value of "#+latex_class:" at the top of your org file, e.g.:

#+latex_class: book-no-parts

Best,

--Diego

On Wed, Nov 28, 2018 at 8:57 PM Ken Mankoff <mankoff@gmail.com> wrote:

Hi Bill,
On 2018-11-28 at 20:42 +0100, William Denton <wtd@pobox.com> wrote:
> Is there a way, exporting as a book, to make Org skip "part" and make
> a top-level Org headline turn into a chapter? Is there a built-in way,
> or do I need to make my own class in org-latex-classes that has the
> structure I want?

What about customizing org-latex-classes?

It contains:

("book" "\\documentclass[11pt]{book}"
("\\part{%s}" . "\\part*{%s}")
("\\chapter{%s}" . "\\chapter*{%s}")
("\\section{%s}" . "\\section*{%s}")
("\\subsection{%s}" . "\\subsection*{%s}")
("\\subsubsection{%s}" . "\\subsubsection*{%s}")))

Seems like modifying that could provide the behavior you're looking for.

-k.