A retention letter usually transmits relevant documents of a single matter (See my post of Aug. 24, 2006 with definitions and distinctions.) whereas outside counsel guidelines lay down ground rules for all matters (See my post of Sept. 25, 2006 that compares these letters to outside counsel guidelines.). The two documents leave an information gap.
The missing information includes (1) a list of acronyms used within the company, (2) the names of key business clients and their roles in the matter, (3) a short history of the business circumstances around the matter, and (4) names and roles of relevant in-house lawyers and paralegals. Supplementing the letter and the guidelines, this context document will help ground a law firm new to the company.