This presentation discusses research on smart cities and open data. It examines the impact of open data on society, business, and public administration. It then describes the MELODA framework, which quantifies the reusability and impact of open data in three stages: by measuring data reusability, creating value from data-driven services, and analyzing citizen experience with those services. The presentation applies this framework to analyze open data from 19 smart cities in Europe, finding that lack of business ecosystem and public entities creating most apps may indicate ecosystem immaturity, and that transportation and traffic data are most popular topics.