How to address a professor in person at US universities? At US universities, how should one address a professor while talking to him or her? In my home country, we usually address the professors as either "sir" or "madam" while talking about our queries in person. 

What's the norm at US universities?
"Professor Lastname" is a sensible default, unless and until the professor asks you to call them something else, or you become aware of local customs that are different.

"Sir" and "Madam" are normally not used.