The first and core objective of City4Age is to enable Ambient Assisted Cities or Age-friendly Cities, where the urban communities of elderly people living in Smart Cities are provided with a range of ICT tools and services that - in a completely unobtrusive manner - will improve the early detection of risks related to cognitive impairments and frailty while they are at home or in the move within the city. The second objective is to provide a range of associated tools and services which - with the appropriate interventions - will mitigate the detected risks. The final objective of C4A is to define a model which will provide sustainability and extensibility to the offered services and tools by addressing the unmet needs of the elderly population in terms of (i) detecting risks related to other health type problems, (ii) stimulating and providing incentives to remain active, involved and engaged, (iii) creating an ecosystem for multi-sided market by matching needs and their fulfillments, (iv) contributing to the design and operation of the ultimate Age-friendly City, where the city itself provides support for detecting risks and providing interventions to those affected by mild cognitive impairment (MCI) and frailty. To achieve these objectives City4Age builds on:- behavioural, sociological and clinical research on “frailty” and MCI in the elderly population;- state of art ICT technology (i) for “sensing” personal data and exposing them as linked open data, (ii) for designing the algorithms and the API’s to extract relevant behaviour changes and correlated risks, and (iii) for designing interventions to counter the risks,- stakeholder engagement in order to be driven by relevant user needs to ensure end-user acceptance.