This lecture will provide the general context for this new and emerging topic, presenting the aims of multiple drone systems, focusing on their sensing and perception. Drone mission formalization, planning and control will be overviewed. Then multiple drone communication issues will be presented, notably drone2ground communication and multisource video streaming. In drone vision, the challenges (especially from an image/video analysis and computer vision point of view), the important issues to be tackled, the limitations imposed by drone hardware, regulations and safety considerations will be presented. A multiple drone platform will be the detailed during the second part of the lecture, beginning with platform hardware overview, issues and requirements and proceeding by discussing safety and privacy protection issues. Finally, platform integration will be the closing topic of the lecture, elaborating on drone mission planning, object detection and tracking, UAV-based cinematography, target pose estimation, privacy protection, ethical and regulatory issues, potential landing site detection, crowd detection, semantic map annotation and simulations. Two drone use cases will be overviewed: a) multiple drones in media production and b) drone-based infrastructure surveillance, notably of electrical installations.