In this cumulative thesis, the author presents four manuscripts and two appendixes. In the manuscripts he discusses mindsets and their relation to the effectiveness of negotiation training. His general claim is that mindsets promise to be relevant for training effectiveness. Still, more research needs to be done and chapter 3 presents the Scale for the Integrative Mindset of Negotiators (SIM) that can be used for some of that research. In the appendixes, the author presents two negotiation training exercises. The first addresses an international refugee policy summit and the second a negotiation over the sale of a large solar pv park in Thailand.