# Chapter 3 Output Formats

The bookdown package primarily supports three types of output formats: HTML, LaTeX/PDF, and e-books. In this chapter, we introduce the possible options for these formats. Output formats can be specified either in the YAML metadata of the first Rmd file of the book, or in a separate YAML file named _output.yml under the root directory of the book. Here is a brief example of the former (output formats are specified in the output field of the YAML metadata):

---
title: "An Impressive Book"
author: "Li Lei and Han Meimei"
output:
bookdown::gitbook:
lib_dir: assets
split_by: section
config:
toolbar:
position: static
bookdown::pdf_book:
keep_tex: yes
bookdown::html_book:
css: toc.css
documentclass: book
---

Here is an example of _output.yml:

bookdown::gitbook:
lib_dir: assets
split_by: section
config:
toolbar:
position: static
bookdown::pdf_book:
keep_tex: yes
bookdown::html_book:
css: toc.css

In this case, all formats should be at the top level, instead of under an output field. You do not need the three dashes --- in _output.yml.