Livability of MediterraneanMediterranean cities is highly challenged by the pressure coming from fast-growing urban expansion and climate-induced hazards. To ensure the wellbeing of its inhabitants, cities need to adopt flexible and dynamic approaches to cope, mitigate and/or adapt to these pressures. In this chapter, we first review population and climate challengesChallenges on the Mediterranean Basin, then we summarize how nature-based solutionsNature-based solutions (NBS) (NBS) promise to be a more flexible alternative than traditional gray infrastructure to reduce the effects of climate change-hazards and support sustainable citiesSustainable cities. We focus in particular on the use of NBS to mitigate urban floodingFloodingand heat wavesHeat waves effects, which are particularly relevant for the Mediterranean region. We then address some of the challengesChallenges connected to the implementation of NBS in the MediterraneanMediterranean: lack of evidence to quantify their short and long-term effectiveness; the difficulty of establishing NBS in dense urban cores with high cultural and historical values; the risks of NBSNature-based solutions (NBS) contributing to inequalities; the need for cross-sector, -actor and -level collaborative governance models; the need for NBS that are resilient to present and future changing conditions; the hidden risk of unintended negative effects of NBS. Lastly, we conclude with some final remarks on the need to collect more empirical evidence of the short and long-term performance of NBSNature-based solutions (NBS) and call for a combined effort of natural and social sciences, stakeholders and industry to advance knowledge on NBS behavior, monitor their efficiency and benefits (or disbenefits) on society and follow up on their performance.