Civil Procedure I
Attorney Work Product
The attorney work product doctrine is a "qualified immunity from discovery" for trial preparation, i.e. efforts by the attorney to investigate and prepare a case.
Technically, it is not a doctrine, not a privilege, but it can still prevent disclosure.
Trial preparation can only be obtained if a party has a substantial need, it can be obtained without undue hardship, and they are unable to obtain substantial equivalent info. Even then, they are not entitled to mental impression of the attorney.