Malpractice is a professional’s failure to use minimally adequate levels of care, skill or diligence in the performance of the professional’s duties, causing harm to another. In New York, attorney malpractice is defined as a "deviation from good and accepted legal practice, where the client has been proximately damaged by that deviation, but for which, there would have been a different, better or more positive outcome."

Malpractice typically occurs when a professional fails to exercise his or her professional skills in an assignment at the necessary standard of care, skill and learning applied under the circumstances by the average prudent reputable member of the profession in the "community". The analysis is based upon the standard of care for the professional in the community" what other professionals in the same field do for their clients who are located in the same geographic area. In New York, courts will hold all attorneys to the same standard of professional performance.

The first necessary element is a professional relationship. In order to sue for professional malpractice, the plaintiff must have retained the attorney. There must of course be a relationship in privity, between the professional and the plaintiff such that the professional owes the plaintiff a duty. In attorney malpractice either a written retainer, proof that the attorney engaged in work or proof that the attorney appeared for the client is necessary. While in litigation often there is clear proof of representation; in transactional settings, representation may be less clear. Proof to a jury’s satisfaction of actual representation must be demonstrated. This proof may come from the correspondence of the professional, from papers authored by the attorney or from litigation documents.