Massachusetts Rules of Professional Conduct Rule 1.9: Conflict of Interest: Former Client
(a) 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 consents after consultation.
(1) whose interests are materially adverse to that person; and
(2) about whom the lawyer had acquired information protected by Rules 1.6 and 1.9(c) that is material to the matter, unless the former client consents after consultation.
(c) A lawyer who has formerly represented a client in a matter or whose present or former firm has formerly represented a client in a matter shall not thereafter, unless the former client consents after consultation:
(1) use confidential information relating to the representation to the disadvantage of the former client, to the lawyer's advantage, or to the advantage of a third person, except as Rule 1.6, Rule 3.3, or Rule 4.1 would permit or require with respect to a client; or
Adopted June 9, 1997, effective January 1, 1998.
 After termination of a client-lawyer relationship, a lawyer may not represent another client except in conformity with this 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. So also a lawyer who has prosecuted an accused person could not properly represent the accused in a subsequent civil action against the government concerning the same transaction.
 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.
Lawyers Moving Between Firms
 When lawyers have been associated within a firm but then end their association, the question of whether a lawyer should undertake representation is more complicated. There are several competing considerations. First, the client previously represented by the former firm must be reasonably assured that the principle of loyalty to the client is not compromised. Second, the rule should not be so broadly cast as to preclude other persons from having reasonable choice of legal counsel. Third, the rule should not unreasonably hamper lawyers from forming new associations and taking on new clients after having left a previous association. In this connection, it should be recognized that today many lawyers practice in firms, that many lawyers to some degree limit their practice to one field or another, and that many move from one association to another several times in their careers. If the concept of imputation were applied with unqualified rigor, the result would be radical curtailment of the opportunity of lawyers to move from one practice setting to another and of the opportunity of clients to change counsel.
 Reconciliation of these competing principles in the past has been attempted under two rubrics. One approach has been to seek per se rules of disqualification. For example, it has been held that a partner in a law firm is conclusively presumed to have access to all confidences concerning all clients of the firm. Under this analysis, if a lawyer has been a partner in one law firm and then becomes a partner in another law firm, there may be a presumption that all confidences known by the partner in the first firm are known to all partners in the second firm. This presumption might properly be applied in some circumstances, especially where the client has been extensively represented, but may be unrealistic where the client was represented only for limited purposes. Furthermore, such a rigid rule exaggerates the difference between a partner and an associate in modern law firms.
 The other rubric formerly used for dealing with disqualification is the appearance of impropriety proscribed in Canon 9 of the ABA Model Code of Professional Responsibility. This rubric has a two-fold problem. First, the appearance of impropriety can be taken to include any new client-lawyer relationship that might make a former client feel anxious. If that meaning were adopted, disqualification would become little more than a question of subjective judgment by the former client. Second, since "impropriety" is undefined, the term "appearance of impropriety" is question-begging. It therefore has to be recognized that the problem of disqualification cannot be properly resolved either by simple analogy to a lawyer practicing alone or by the very general concept of appearance of impropriety.
 Preserving confidentiality is a question of access to information. Access to information, in turn, is essentially a question of fact in particular circumstances, aided by inferences, deductions or working presumptions that reasonably may be made about the way in which lawyers work together. A lawyer may have general access to files of all clients of a law firm and may regularly participate in discussions of their affairs; it should be inferred that such a lawyer in fact is privy to all information about all the firm's clients. In contrast, another lawyer may have access to the files of only a limited number of clients and participate in discussions of the affairs of no other clients; in the absence of information to the contrary, it should be inferred that such a lawyer in fact is privy to information about the clients actually served but not those of other clients.
 Application of paragraph (b) depends on a situation's particular facts. In such an inquiry, the burden of proof should rest upon the firm whose disqualification is sought.
 Paragraph (b) operates to disqualify the lawyer only when the lawyer involved has actual knowledge of information protected by Rules 1.6 and 1.9(b). Thus, if a lawyer while with one firm acquired no knowledge or information relating to a particular client of the firm, and that lawyer later joined another firm, neither the lawyer individually nor the second firm is disqualified from representing another client in the same or a related matter even though the interests of the two clients conflict. See Rule 1.10(b) for the restrictions on a firm once a lawyer has terminated association with the firm.
 Independent of the question of disqualification of a firm, a lawyer changing professional association has a continuing duty to preserve confidentiality of information about a client formerly represented. See Rules 1.6 and 1.9.
 The second aspect of loyalty to a client is the lawyer's obligation to decline subsequent representations involving positions adverse to a former client arising in substantially related matters. This obligation requires abstention from adverse representation by the individual lawyer involved, but does not properly entail abstention of other lawyers through imputed disqualification. Hence, this aspect of the problem is governed by Rule 1.9(a). Thus, if a lawyer left one firm for another, the new affiliation would not preclude the firms involved from continuing to represent clients with adverse interests in the same or related matters, so long as the conditions of paragraphs (b) and (c) concerning confidentiality have been met.
 Information acquired by the lawyer in the course of representing a client may not subsequently be used or revealed by the lawyer to the disadvantage of the client or to the advantage of the lawyer or a third party. See Rule 1.8(b) and Comment 1A to that Rule. However, the fact that a lawyer has once served a client does not preclude the lawyer from using generally known information about that client when later representing another client.
 Disqualification from subsequent representation is for the protection of former 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.
 With regard to an opposing party's raising a question of conflict of interest, see Comment to Rule 1.7. With regard to disqualification of a firm with which a lawyer is or was formerly associated, see Rule 1.10.
Corresponding ABA Model Rule. Identical to Model Rule 1.9 except for (c).
Corresponding Former Massachusetts Rule. DR 4-101 (B) and (C), DR 5-105; (c) no counterpart.
Cross-reference: See definition of "consultation" in Rule 9.1 (c).