This book introduces community science (or citizen science) projects in Japan with a focus on ecology. Environments and ecosystems that have been slowly built up over time are changing and collapsing dramatically. In this rapidly changing environment, ecologists need to collaborate with volunteers in their research and activities to investigate and conserve a vast area. This book aims to guide ecologists in the practice of community science. The authors, who are leading ecologists and practitioners of community science projects, share their methods and lessons learned from practice.  The book begins with the definition of community science and the following chapters introduce monitoring in ecological community science, using various methods such as observation, specimens, photographs, videos, sounds, and environmental DNA. Readers can learn about the advantages and disadvantages of these methods in ecological community science monitoring. The book also coverstopics such as scientific communication, data obtained from ecological community science monitoring, the rights of participants, decision-making in community science, and conservation activities with volunteers such as invasive alien species extermination and nature restoration.  This book serves as a valuable resource for readers interested in ecological community science and its practice. The book is suitable for both undergraduate students and researchers as well as practitioners.