Here's a bit from FMCS:
A Different Way to Negotiate
Known by many names and practiced in many variations and settings: Win-Win Bargaining, Mutual Gains, Principled or Interest-Based Negotiation, Interest-Based Problem Solving, Best Practice or Integrative Bargaining. No matter which variation is used, Interest-Based Bargaining (IBB) may offer parties more flexibility than traditional bargaining, not locking them into predetermined issues and bargaining positions. Instead, the process begins with understanding the problem and identifying the interests that underlie each side’s issues and positions.