The binary positions of day versus night find themselves condensed in cities where strategies and tactics to recalibrate the nocturnal city are abundant. A number of these concern boundaries that seek to promote and protect certain ways of being in the city whilst explicitly demarcating and prohibiting other forms. One of the key points here is the disappearance of the nocturnal city as it undergoes processes to comprehensively absorb it within the rules and regulations that make cities so successful during the day. In his book 24/7 Crary (2013) explores some of the paradoxes of the expanding, non-stop life-world of twenty-first century capitalism – paradoxes that are inseparable from shifting configurations of sleep and waking, illumination and darkness, justice and terror, and from forms of exposure, unprotectedness, and vulnerability. With recent renewed interest on the nighttime economy and appointment of night mayors, the pressure on cities to maximise their opportunities, investment and activity is growing. The nighttime city remains a frontier which is poorly understood and as architects and urbanists there are important questions about how we might respond to it. This talk will explore questions about our environment, our lives and the future sustainability of our cities.