The "duty to mitigate loss" doctrine has been the object of study in many jurisdictions, which have interpreted and applied it in a wide range of situations and in different ways. In Brazil, however, only recent discussions have brought light to this subject. Worldwide, researchers have debated its nature - whether a duty or a principle - and the most proper way to address it (e.g.: if duty to mitigate loss or damages; duty to rescue; avoidable consequences doctrine). Studies have also detailed its application in different situations, such as in contracts and torts, among suppliers, consumers and national and international commerce, for instance. Ultimately, responding to the shift for globalized relations involving parties from different jurisdictions, the development of the doctrine and its standardization by Common Law courts, Civil Law codifications and international rules have allowed emerging countries to take advantage of the lessons learnt in more experienced systems and helped them regulate their own in the most suitable form. The purpose of this book is to provide an in-depth study of the "duty to mitigate loss" - from its origin to its current application in selected jurisdictions - so as to comprehensively come up with a proposition that is sufficiently adequate to fill the Brazilian legal framework gap diagnosed with respect to its effective regulation.