This book presents the development and field application of an integrated UAV and UGV system for the exploration and monitoring of active volcanoes in the Philippines. It offers a practical and research-driven approach to addressing the challenges of collecting environmental data in highly hazardous and inaccessible volcanic terrain. Designed for researchers, engineers, and professionals in robotics, geoscience, and disaster response, this book introduces a semi-autonomous aerial-ground system capable of deploying and retrieving a ground robot using a drone and tether mechanism. It also features the use of drone-based gas sensing for real-time volcanic emission monitoring and a drone-mounted water sampler for collecting samples from crater lakes. This book covers system design, control architecture, communication strategies, and results from simulated and real-world field tests. By combining autonomous systems and sensor technologies, this book provides an innovative solution to support safer and more effective volcanic exploration and geohazard assessment.