urban sustainability indicators and processes designed to be implemented across different contexts. This may suggest that a process of eco-city 'standardization' is underway. Practical limits Richard Register once stated that "An ecocity is an ecologically healthy city. No such city exists". Despite the conceptual ecological benefits of eco-cities, actual implementation can be difficult to attain. The conversion of existing cities to eco-cities is uncommon because the infrastructure, both in terms of the physical city layout and local bureaucracy, are often major insurmountable obstacles to large-scale sustainable development. The high cost of the technological integration necessary for eco-city development is a major challenge, as many cities either can't afford, or are not willing to take on, the extra costs. Such issues, along with the added challenges and limits to retrofitting existing cities contribute to the establishment of newly constructed eco-cities. Along with this, the costs and infrastructure development needed to manage these large scale, two-pronged projects extend beyond the capabilities of most cities. In addition, many cities around the world are currently struggling to maintain the status quo, with budgetary issues, low growth rates, and transportation inefficiencies, that encourage reactive, coping policies. While there are many examples worldwide, the development of eco-cities is still limited due to the vast challenges and high costs associated with sustainability. Related terminologies Eco-cities have been developed as a response to present-day unsustainable systems that exist in our cities. Simultaneously, there have been other concepts like smart cities, sustainable cities, and biophilic cities that also strive towards achieving sustainability in cities through different approaches. Owing to ambiguity in their definitions and closely related criteria defined to achieve their goals, these concepts, despite their varying approaches, are often used interchangeably. Criticism Three pitfalls Looking at the patterns of progress in the last few decades of city construction towards sustainability, Valaria Saiu (University of Cagliari) poses one major criticism through the existence of a theory-practice gap caused by economic and ethical conflicts and risks that generate socio-spatial utopias. She identifies three pitfalls in the concept of sustainable cities (and therefore, eco-cities): The Idea of the City as a Business: "Most eco-city projects are dependent on technologies available on the global market and the city is considered as a big economic affair". Often developed as techno-centric concepts, these projects seek investment opportunities by public-private partnerships leading to a top-down approach. This structure lacks democratic approaches in the decision-making process