From the YALSA Website:
The Committee shall consist of a chair, eight members, a consultant from the staff of Booklist, and an administrative assistant if the Chair requests. Beginning in 2002, the Chair and four members will be appointed by the Vice President/ President-Elect of YALSA. The remaining four members will be elected by the membership of the Association.
Members serve two-year terms beginning immediately after Annual and ending after Annual of the announcement year. All members are required to attend all Printz Committee meetings held during the selection process. In the event a member is unable to complete her/his term, the President of the Association shall appoint a replacement from among the members of the Best Books for Young Adults Committee.
The chair is a voting member of the committee with all the rights and responsibilities of other members. In addition, the chair presides at all meetings of the committee and serves as a facilitator of both discussion and committee business. As such, the chair must serve as a list owner of an electronic discussion list created through the YALSA office solely for use by the committee, and take responsibility for list maintenance. The chair has sole responsibility for any contact with publishers.
In consultation with the Chair, the Vice President/President-Elect may appoint an administrative assistant for the term. The administrative assistant is not a voting member.
The Editor/Publisher of Booklist magazine, the Printz Award's sponsor, will appoint a consultant to the Committee from among the magazine's Books for Youth staff. This consultant may participate fully in all book discussions but may not participate in voting.
The 2009 Committee, including Chair and Administrative Assistant, are listed at the YALSA Website. As you can see, half are elected; half are nominated. I was elected; eight people ran, and four were elected. This year. Carlie Webber (a contributor here at Tea Cozy) is running. To vote, you need to be a member of YALSA (and, I believe, a member as of January 1, 2008). When the ALA elections open, I'll post the full slate.
I think it's interesting that the substitute for the Printz is drawn from Best Books; it makes sense, under the assumption that a BBYA member is more likely than not to have read the eligible books. I guess I'll be careful around any BBYA members!