Agreement typically between two parties on the same side of a lawsuit, usually both defendants (but sometimes and indemnifier and the beneficiary of the indemnity (or indemnitee/indemnified)), that allows their counsel to exchange information and discuss strategy, while preserving attorney client privilege. JDA’s are particularly important when in U.S. litigation or when U.S. litigation is threatened. If joint parties communicate otherwise attorney-client-privileged information without a JDA, there is a substantial risk that a court will hold the communications non-privileged.
For a JDA to be valid there must be a community or commonality of legal interest, e.g., parties should usually be defending the same or very similar claims, for example the same patent; JDA’s can also be executed between a defendant/indemnitee and the indemnifier. Usually a JDA will, especially in the case of an indemnifier-indemnified relationship specifically provide that its sole purpose is the protection of privilege and preclude any other changes in the contractual/indemnity relationships between the parties. It is important to be aware that any statements made or information exchanged between the parties before the JDA is reached do not benefit from privilege. Moreover the parties’ counsel should be part of the communication loop. A JDA is sometimes also called a Common Interest Agreement or Community of Interest Agreement.
Common interest agreements are also sometimes used in disclosing privileged information during due diligence for corporate transactions. US case law is split on the effectiveness of such agreements at preserving privilege, but if legal positions that might be relevant to litigation must be discussed such an agreement should usually be signed first.