The University of Washington has many local chapters for honorary societies. The HUB's Registered Student Organization (RSO) website is the best place to find comprehensive listings and contact information for these groups. The UW Honors Program does not have any direct affiliation with these societies; please contact the campus representative with any questions you may have.
If you've been invited to join an honor society, be sure to research the organization before joining or submitting any membership fees. There are many online resources available that will help you determine if a particular honor society is right for you.
If you are still in doubt, contact the University of Washington campus representative of that honor society, who should be named in your letter of invitation.