Visiting Scholar
A Visiting Scholar appointment is a courtesy appointment without salary for up to two years. A Visiting Scholar must hold a professorial title at another institution.
Visiting Scholar Request Form

Visiting Scientist
A Visiting Scientist appointment is a temporary appointment that can be with or without salary. The visitor cannot be enrolled as a student at another institution, nor can they be eligible for a postdoctoral scholar appointment instead. A master’s degree is required. The max appointment length for a Visiting Scientist is 3 months for US Citizens and 2 years for non-US citizens.
Visiting Scientist Request Form

Visiting Student/VISIT
If you will have a currently enrolled student visit your lab, they will need to come through the University's VISIT program. Please talk to the HR manager regarding the VISIT program and the rules and regulations. VISIT stipends may not be paid on an externally funded award unless the award sponsor specifically approves payment of a stipend to an international visitor.
https://www.ielp.uw.edu/programs/research-programs/visit/overview