Rules of Professional Conduct
Rule 1.9: Conflict of Interest: Former Client
A lawyer who has formerly represented a client in a matter shall not thereafter represent another person in the same or a substantially related matter in which that person’s interests are materially adverse to the interests of the former client unless the former client gives informed consent.
 After termination of client-lawyer relationship, a lawyer may not represent another client except in conformity with the Rule. The principles in Rule 1.7 determine whether the interests of the present and former client are adverse. Thus, a lawyer could not properly seek to rescind on behalf of a new client a contract drafted on behalf of the former client. Similarly, a lawyer who has defended a client against charges brought by a regulatory agency concerning a transaction may not later represent another client in a private lawsuit against the client involving the same transaction, absent the first client’s informed consent. For the definition of “informed consent,” see Rule 1.0(e).
 The scope of a “matter” for purposes of this rule may depend on the facts of a particular situation or transaction. The lawyer’s involvement in a matter can also be a question of degree. When a lawyer has been directly involved in a specific transaction, subsequent representation of other clients with materially adverse interests clearly is prohibited. On the other hand, a lawyer who recurrently handled a type of problem for a former client is not precluded from later representing another client in a wholly distinct problem of that type even though the subsequent representation involves a position adverse to the prior client. Similar considerations can apply to the reassignment of military lawyers between defense and prosecution functions within the same military jurisdiction. The underlying question is whether the lawyer was so involved in the matter that the subsequent representation can be justly regarded as a changing of sides in the matter in question. Rule 1.9 is intended to incorporate District of Columbia and federal case law defining the “substantial relationship” test. See, e.g., Brown v. District of Columbia Board of Zoning Adjustment, 486 A.2d 37 (D.C. 1984) (en banc); T.C. Theatre Corp. v. Warner Brothers Pictures, 113 F. Supp. 265 (S.D.N.Y. 1953), and its progeny.
 Matters are “substantially related” for purposes of this rule if they involve the same transaction or legal dispute or if there otherwise is a substantial risk that confidential factual information as would normally have been obtained in the prior representation would materially advance the client’s position in the subsequent matter. For example, a lawyer who has represented a businessperson and learned extensive private financial information about that person may not then represent that person’s spouse in seeking a divorce. Similarly, a lawyer who has previously represented a client in securing environmental permits to build a shopping center would be precluded from representing neighbors seeking to oppose rezoning of the property on the basis of environmental considerations; however, the lawyer would not be precluded, on the grounds of substantial relationship, from defending a tenant of the completed shopping center in resisting eviction for nonpayment of rent. Information that has been disclosed to the public or to other parties adverse to the former client ordinarily will not be disqualifying. Information acquired in a prior representation may have been rendered obsolete by the passage of time, a circumstance that may be relevant in determining whether two representations are substantially related. In the case of an organizational client, general knowledge of the client’s policies and practices ordinarily will not preclude a subsequent representation; on the other hand, knowledge of specific facts gained in a prior representation that are relevant to the matter in question ordinarily will preclude such a representation. A former client is not required to reveal the confidential information learned by the lawyer in order to establish a substantial risk that the lawyer has confidential information to use in the subsequent matter. A conclusion about the possession of such information may be based on the nature of the services the lawyer provided the former client and information that would in ordinary practice be learned by a lawyer providing such services.
 Disqualification from subsequent representation is for the protection of clients and can be waived by them. A waiver is effective only if there is disclosure of the circumstances, including the lawyer’s intended role in behalf of the new client. The question of whether a lawyer is personally disqualified from representation in any matter on account of successive government and private employment is governed by Rule 1.11 rather than by Rule 1.9.
 With regard to disqualification of a firm with which a lawyer is associated, see Rules 1.10; for former government lawyers, see Rule 1.11; for former judges and law clerks, see Rule 1.11.