The Independent Self-Publishers Alliance is a relatively new professional organization for authors who self-publish. Of the organizations I have reviewed thus far, it also the one I find the most interesting. Also of note, it is an organization that has a subtle sense of humor which I think has a lot to do with the individuals who founded it.
Its membership requirements are also different from the other professional organizations for small publishers and self-publishing authors. You must have self-published either a paper book or an ebook. The requirements for membership below were taken directly from the ISPA's website.
The membership requirements for the Independent Self-Publishers Alliance are very simple, and there are two classes of membership with equal benefits:
(1) Self-publisher (i.e., author and publisher) of at least one printed book ("pBook") or electronic book ("eBook").
(2) Non-self-publisher who supports self-publishing (such as a designer, editor, publicist, consultant or author of a book or operator of a website that will help self-publishers).
To prove that you are the publisher of a printed book please send an email to email@example.com with a link to a bookseller's website that shows you as the author of the book, as well as some means of identifying you or your company as the owner of the ISBN associated with the book.
Because ISBNs are not necessary for eBooks, membership requirements for people who self-publish eBooks but not pBooks are simpler. Please send an email to firstname.lastname@example.org with a link to a bookseller's website that shows you as the author of the eBook, as well as some means of identifying you or your company as the publisher.
Books that identify vanity presses as publishers are not acceptable. The officers of the association have the final say on such determinations.
For a type-2 membership, please send an email with an appropriate link to email@example.comAs an author who self-publishes, I found this site to be very helpful. It contains much of the usual information that one can expect to find on the website of a professional organization. It also has a great deal of information that is actually useful to an author, regardless of whether or not the author is self-publishing for the first time.
One of the stances ISPA takes also makes it unusual. The organization clearly makes a determined effort to educate aspiring authors who are planning to self-publish to be aware of the pitfalls of vanity publishing companies. The organization also provides information about how to truly self-publish.
There is too much specialized information on the site to cover it all in this short summary so I suggest you simply visit the site at http://www.independentselfpublishers.org/