Integrated Urban hydrometeorological, climate and environmental Services (IUS) is a WMO initiative to aid development of science-based services to support safe, healthy, resilient and climate friendly cities. Guidance for Integrated Urban Hydrometeorological, Climate and Environmental Services (Volume I) has been developed with the intent to provide an overview of the concept, methods and good practices for producing and providing these services to respond to the hazards across a range of time scales (weather to climate). This involves combining (dense) heterogeneous observation networks, high-resolution forecasts, multi-hazard early warning systems and climate services to assist cities in setting and implementing mitigation and adaptation strategies for the management and building of resilient and sustainable cities. IUS include research, evaluation and delivery with a wide participation from city governments, national hydrometeorological services, international organizations, universities, research institutions and private sector stakeholders. An overview of the IUS concept with key messages, examples of good practice and recommendations are provided. The research community will play an important role to: identify critical research challenges; provide impact forecasts and warnings; develop and deliver IUS internationally, and; support national and local communities in the implementation of IUS thereby contributing to the United Nations' Sustainable Development Goals at all scales. 2015-2030 (UNDRR, 2015) aims to substantially reduce impacts of disaster in terms of mortality, economic loss and damages, and disruption of basic services, while contributing to the mitigation of technological and security risks, through the provision of impact-based services (WMO, 2016). These services consider hazards, vulnerability and exposure. Governments, businesses and the public need to understand how the hydrometeorological hazard may affect their lives, livelihoods, property and economic activity in order to take appropriate actions. As weather, air quality, climate and the water cycle know no national boundaries, international cooperation at a global scale is essential to develop commensurate services and to reap the benefits from their application. The WMO, a United Nations Specialized Agency, provides the framework for such international cooperation. This intergovernmental organization's 193 member states and territories (called Members) are mainly concerned with issues at a national, regional and international J o u r n a l P r e -p r o o f Journal Pre-proof the Guidance (Vol. 1) for the broader scientific community and stakeholders. Following a background discussion (section 2), the IUS concepts are outlined (section 3). Results from surveys of urban experts and WMO members (section 4) are used to articulate the science and knowledge gaps (section 5) and to illustrate the lessons learnt and recommendations (section 6). This is followed by concluding remarks (section 7).J o u r n a l P r e -p r o o f Journal Pre-proof ...