Interests are what compel people to negotiate. Interests lie behind positions. Interests may include a party's desire for economic security, military security, political recognition/legitimacy, sovereignty, political autonomy or representation, sustenance, or specific underlying goals that motivate the person or party to seek concessions or acceptable solutions to a dispute, problem, or business opportunity.
Interests are what a party in a dispute cares about or wants. They are the underlying desires and concerns that motivate people to take a position. While people's positions are what they say they want (such as "I want to build my house here"), their interests are the reasons why they take a particular position ("because I want a house close to my family"). Parties' interests are often compatible, and hence negotiable, even when their positions seem to be in complete opposition.