Tenure-track faculty usually serve on one standing committee after the first year. You will find that requests for other service to the college (e.g., ad hoc committees, admissions work, advisor to student clubs) tend not to be restricted by the terms of your appointment and they will often take more of your time than service on standing committees. Be prepared for many requests from students, faculty, staff and administrators, particularly if you fit a particular description (e.g. untenured female scientist) and/or have a particular expertise. If we said yes to all that we were asked to do at Knox, we would not have enough time for teaching, research or ourselves. Saying no to some of the requests will preserve your sanity and may help decrease, overall, the requests that are made of us. Talk to some of your colleagues about how much service they do for the college to gauge your level of participation.