Hello all, I've heard various opinions on this topic, so I thought I would open it up to a wider audience: I am entering a PhD program this fall, and am just curious about proper etiquette. As an undergrad, I always referred to my mentors and professors as Dr. So-and-so, or Professor So-and-so. Typically, if corresponding via email, I would simply address them however they signed their emails. Once, however, my QM professor signed it with just her first name. She later wanted to clarify that she meant to sign "Professor" and not just her first name. I honestly hadn't even noticed, but wondered if that was some widely accepted method of showing acceptance of being on a first-name basis. I am especially curious because as I email my new mentors and professors, they nearly always sign their first name only. I do not want to use improper etiquette, but I also don't want to appear like I do not pay attention to detail, or ignore invitations to address them differently. What is common practice, or your opinions? Thanks!