In general, attorneys registered with the Luxembourg Bar (avocats liste II and liste IV and avocats à la Cour) ("Luxembourg attorneys") are subject to an obligation of absolute professional secrecy under the Luxembourg Bar Regulation (Règlement Intérieur de l'Ordre des Avocats de Luxembourg (RIO)).

Luxembourg attorneys cannot disclose confidential client information or legal opinions provided to clients. Although there is no formal definition of confidential client information, experience has shown that client confidential information includes any and all information provided by a client in any form whether written–electronic, physical documents, exhibits or oral (letters, email, telephone conversations, tapes, photographs, electronic documents, etc.). The duty to maintain confidentiality extends to any information that the lawyer has obtained from the client or third party as a result of being instructed on a matter, whether or not the information concerns the client and/or a third party.

Communications between a Luxembourg attorney and their client — whether to advise or to defend — are covered by legal privilege. A breach of duty by a Luxembourg attorney constitutes professional misconduct and a criminal offense.^[1] A Luxembourg attorney may disclose confidential client information only when defending themselves against a charge alleged by the client. A client may also disclose information with no limitation. The client is entitled to waive the confidentiality covering a document and decide whether to disclose it. Based on such waiver, a lawyer is then entitled to disclose the document with express consent from the client.

Communications between Luxembourg attorneys are privileged and their contents may not be divulged to the courts unless such communications have been labelled as "official" or are to be considered as official by their nature.

Under Luxembourg ethical rules, in-house counsel are not subject to the obligation of professional secrecy. Thus, in-house counsel are also not subject to legal privilege.

Communications between Luxembourg lawyers and foreign lawyers are only privileged if specially marked as such and comply with the rules applicable for each of the jurisdictions concerned (see as an example the European code of conduct - article 5).

[1] See Luxembourg Criminal Code (Article 458).