Can a Guest Lecturer be my Referee? I have a guest lecturer who taught me one module for one semester and graded my work. He is willing to be my referee. Would he be counted as an acceptable referee if I were applying to be admitted for a PhD (graduate admission)?

Edit: I would like to mention that I asked because I was just worried because I don't know if it's standard practice to accept such referees even if they have taught me for one full semester, and some bureaucrats who may act as gatekeepers to academic staff might err on the side of caution almost to the point of inflexibility.
Can a Guest Lecturer be my Referee?


Yes, they can. To determine if they are the best referee for a graduate application, try answering the following questions:


Can this person attest for my strong research potential? (Not just performance in coursework) (e.g. did you talk to them after lecture about ideas outside the scope of the course? Did they seem interested in discussion research-level topics with you?)
Will this person's name (or at least their University affiliation) be recognized by the admissions committee or by the professors whose groups you apply to?


If the guest lecturer satisfies one or both of those criteria, they could be a good choice. If they don't satisfy them, see if there is someone else who would satisfy them. It is still a trade-off here -- someone who knows you better is more likely to give a good letter than someone who does not know you as well. It may be that the guest lecturer is the best choice even if they do not satisfy these criteria, in the case that no one else really does either.