A dialogue between individuals or organizations to arrive at common ground, resolve a difference, or share resources is an essential part of the business process. Why name business alone, negotiation is a skill that is required in every sphere of life.
Trained negotiators exist for almost every situation, e.g., negotiators handling hostage situations or working with unions. Even a psychologist talking to a would-be suicide on a high roof is negotiating. In any of the situations listed above and other similar ones where the stakes are very high, a professional negotiator would be needed. With a few common sense rules, however, even an untrained person can be a fairly good negotiator.