The Business, Science & Industry Department located in Central Library has the "Directory of Physicians in the United States" (American Medical Association) and  the "Official ABMS Directory of Board Certified Medical Specialists."  You can come into the department, or call at 215-686-5394 to get information about a physician.

The State of Pennsylvania Bureau of Professional and Occupational Affairs also maintains a searchable, online database of professional licenses.  You can verify that your physician holds a valid license by visiting: http://www.licensepa.state.pa.us/