This project aims to address several scientific and technological challenges towards fast package delivery in urban environments using drones. As there are severe autonomy constraints to the endurance and travel distance of drones, this project will explicitly consider those limitations and use drone relays to enable effective package delivery to destinations that go beyond the flight range and autonomy of a single drone. Interestingly enough, this raises other scientific challenges in terms of planning of optimal and efficient trajectories for a team of drones deployed throughout a city, for the cooperative control of several drones for package transportation and relay maneuvers, as well as for estimation of vehicles and package location during transportation and relay maneuvers. The research plan will start by addressing single vehicle control and estimation strategies, and progressively evolve into cooperative control, estimation and planning for coordinated relay transportation.