Many different potential theories exist for plaintiffs who believe they have been harmed by  attorneys.

In almost every circumstance, the client has an agreement, whether it is reduced to writing or not, with an attorney. Therefore, depending on the terms of the contract, the client could potentially have a claim sounding in breach of contract. A breach of contract claim typically requires that the plaintiff have a valid contract (written or oral), that the plaintiff performed its obligations, that the defendant breached, and the breach caused damages.

Attorneys can also be sued under a breach of fiduciary duty theory.  Under this theory, attorneys owe fiduciary duties to their client, including the obligations of fidelity, honesty, and good faith, and if they breach this duty and cause damages to a client, the client may be able to bring a claim. Claims for breach of fiduciary duty are sometimes used when an attorney places his or her interest above that of a client. One notable aspect of a claim for breach of fiduciary duty is that there may be no ability to have a jury hear the case.

Most commonly, attorneys are sued for professional negligence or legal malpractice. This requires that a lawyer owes a duty to a client, the lawyer breaches the duty, and the breach causes damages. This is the most frequent claim under which lawyers are sued by their clients in Illinois and is the claim discussed by many cases involving legal malpractice.

Sometimes, more than one claim is pled in the same complaint. Illinois law provides, however, where both fiduciary duty claims and professional negligence claims are brought against a lawyer are supported by the same operative facts and rely on the same injury, one may be dismissed. Therefore, if more than one claim is pled, the claims should be based on different facts or injuries.