I'm currently beginning research that involves an aspect of Professional Development (PD) for Mathematics teachers, but I don't have much experience or knowledge of PD. What are some of the seminal works on PD for Mathematics teachers that I can include in my Literature Review?
In terms of researchers who I am personally familiar with: I would recommend work by Orit Zaslavsky.
From her NYU-Steinhardt bio:
A search in google scholar here has as its top two citations:
For mathematics teachers in general (as opposed to mathematics teacher-educators) see if you can track down the 1994 NCTM yearbook, which had as its focus (and title) "Professional Development for Teachers of Mathematics." It's already 20 years old, but should provide a good starting point.
(Incidentally, checking google scholar for articles on PD that cite the '94 yearbook yields the latter of Zaslavsky's articles cited above as the first result.)