The book "(Un) sustainable city" is a compilation of texts, published in parallel with the number 91 of the magazine Arquine and within the framework of the 7th edition of MEXTRÓPOLI, Festival de Arquitectura y Ciudad, that deal with the problem of the climate crisis, some of its causes and its effects and in different ways how we can address it. The territory and the city, the atmosphere and its preservation, the architecture versus the construction, are some of the topics covered by these nine essays written from different disciplines and geographies. The publication seeks to find a "more hopeful" future and its title should be understood as a double ultimatum, as it reflects not on what has not happened in just over 10 years (of the first publication by Arquine on the subject) but on tiny emerging practices, such as recycling and reconstruction that have happened in multiple geographies and cities as part of the new green agenda.