Doctors are often asked for information about their patients by third parties (employers, government agencies, insurance companies, regulatory bodies, and many others). Any doctor may receive such requests, but in the United Kingdom they come most often to general practitioners (table 1)⇓ because general practices hold the most comprehensive patient records.

A form may need to be filled out, or the doctor needs to write a letter. The response may be a certificate, a statement, or a report; this makes no difference and I will call them all reports. Some are straightforward, but others pose difficulties: conflicts of interest between patients and third parties, uncertainty about the information the doctor possesses and how to present it, and problems about payment. Classifying them may help us understand the problems better.