During the Middle Ages, government is a game of negotiation between power holders. Concepts such as the common good, power of the people, conciliarism, universities, and double rule (mere and mixed empire) were used in an era when negotiation, justifying speeches, and ostentation (at different levels and social strata) ended up imposing themselves. The sovereign had to deal with certain collectives by claiming that he spoke on their behalf. Thus, contractual monarchy and representativeness were key contributions of the Middle Ages. The evidence of these realities can be found in art, literature, archaeology, and documentation… The researcher only needs to examine them. The International Medieval Meeting Lleida invites all attendants to take an interdisciplinary approach to explore this important point in history.