Books can be published in five main ways:

1. Traditional publishing: They pay authors an advance.
2. Small presses. They pay no advance and avoid print runs.
3. Assisted and hybrid publishing. Authors pay to publish.
4. Indie or DIY self-publishing. Authors start their own publishing company.
5. Social publishing. Authors build a readership online.

Some PEG members are publishers. Check the Find an Editor and Job Submission pages and search for .

Jane Friedman gives a lot more information here.