The two protections that keep what a client tells a lawyer, and what a lawyer prepares for a case, from being forced into evidence - what the privilege covers and what it does not, who holds it and how it is waived, the crime-fraud exception, the separate and narrower work-product doctrine, and how each is asserted in discovery.
The attorney-client privilege protects confidential communications between a client and a lawyer made for the purpose of obtaining or providing legal advice. It belongs to the client, not the lawyer; it survives the end of the representation and, in most jurisdictions, the client's death; and it permits the client to refuse to disclose, and to prevent the lawyer from disclosing, the communication itself. The protection has limits that are often misunderstood. It covers communications, not facts: a client cannot make a fact privileged by telling it to a lawyer, and can be asked about the fact in a deposition, only not about what was said to counsel. It requires confidentiality: a conversation in the presence of a third party who is not needed for the advice, an email copied to a friend, or a document later shown to others is not protected. It requires a legal purpose: business advice, a lawyer acting as a negotiator or scrivener, and communications with a lawyer who is not acting as a lawyer fall outside it. And it does not cover the identity of the client, the fee arrangement, or the fact that a consultation occurred, except in unusual circumstances.
A corporation holds the privilege for communications between its lawyers and its employees made to obtain legal advice for the company, at the direction of management and within the scope of the employee's duties, and the company - not the employee - controls it, which is why in-house counsel warn employees that the privilege is the company's. The privilege is waived by voluntary disclosure of the communication to an outsider, and a waiver can extend to other communications on the same subject where fairness requires; it is also waived by a client who puts the advice in issue, for instance by claiming to have relied on counsel. An inadvertent production in discovery does not waive the privilege if reasonable steps were taken to prevent and to correct it, and litigants commonly agree to a clawback order in advance. The crime-fraud exception withdraws protection from communications made in furtherance of a crime or fraud the client intended to commit, whether or not the lawyer knew; the exception applies to future or ongoing wrongdoing, not to a client's confession of a completed one, which is exactly what the privilege exists to protect. Related privileges cover communications through the lawyer's staff, interpreters and consulting experts, and parties with a common legal interest may share privileged material under a joint-defence agreement without waiving it as to outsiders.
Work product is a separate doctrine, created by the rules of procedure rather than the law of evidence, protecting materials prepared by or for a party or its representative in anticipation of litigation: the lawyer's notes, memoranda, witness interviews, investigation and strategy. Ordinary work product may be obtained only on a showing of substantial need and an inability to get the equivalent without undue hardship; opinion work product - the lawyer's mental impressions, conclusions, opinions and theories - is almost absolutely protected. Unlike the privilege, work-product protection belongs to the lawyer as well as the client, is not waived by disclosure to a friendly third party, and covers documents prepared by investigators, insurers and consultants as well as by counsel; but it reaches only materials prepared because of prospective litigation, so a report an insurer or a business would have prepared in the ordinary course is not protected. Both protections are claimed in discovery by withholding the document and describing it in a privilege log with enough detail for the other side to assess the claim, and a court decides any dispute, often after reviewing the document privately.
The practical advice is short: tell the lawyer everything, in private, and do not repeat the conversation to anyone else, because candour is protected and disclosure destroys the protection. Employees interviewed by company counsel should understand whose privilege it is and ask whether they need their own lawyer. Anyone facing discovery who has documents involving lawyers, insurers or investigators needs counsel to review them before production, to log what is withheld, and to negotiate a clawback order, since an inadvertent production without one can be argued as a waiver. A person who suspects a lawyer's advice was used to further a fraud should know that the crime-fraud exception exists and that the privilege will not hide it.
Choose your state. Each link opens the directory page for the city in that state with the most currently published law firms in this practice area; a +n beside the city is how many other cities in the state also have one. The list is generated when this page loads, so a state whose listings have lapsed drops out rather than becoming a dead link.