Exempt Staff - employees whose responsibilities are primarily executive, managerial, or administrative, or whose positions require an advanced educational degree or knowledge and experience in a field considered professional. These positions are paid monthly and are exempt from the overtime requirements of the Fair Labor Standards Act (FLSA) that mandate overtime pay for time worked in excess of 40 hours per week.
Non-Exempt Staff - employees holding positions in support activities. Employees in these jobs are not exempt from the Federal labor Standards Act (FLSA) overtime provisions and they are paid by the hours and are paid 1½ times their regular pay rate for hours worked in excess of 40 in a week. (source - Human Resources Staff Handbook)
http://www.library.northwestern.edu/node/2095

Technical and support staff (who do not meet the criteria of the Fair Labor Standards Act for professional, executive, or administrative staff) are paid the federally required overtime rate for hours worked in excess of 40 in any pay week.
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Professional, executive, and administrative staff (who meet criteria set forth in the Fair Labor Standards Act) are not eligible for overtime pay.
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http://www.professor.rice.edu/professor/Pay_PracticesHours_o...