In the past few decades, the field of ecology has made huge advancements thanks to stable isotopes. Ecologists need to understand the principles of stable isotopes to fully appreciate many studies in their discipline. Ecologists also need to be aware of isotopic approaches to enrich their “toolbox” for further advancing the discipline. A Primer on Stable Isotopes in Ecology is a concise and foundational resource for anyone interested in acquiring theoretical and practical knowledge for the application of stable isotopes in ecology. Readers will gain a more in-depth and complete knowledge of stable isotopes and explore isotopic methods used in ecological research, learning about stable isotope definitions, measurement, ecological processes, and applications in research. Chapters include in-depth descriptions of stable isotopes and their notation, isotope fractionation, isotope mixing, heavy isotope enrichment, and quantification methods by mass spectrometry and laser spectroscopy. The text guides readers to think "isotopically” to better understand research conducted using stable isotopes. The book also provides basic practical skills and activities to apply stable isotope methods in ecological research. It includes 5 activities through which readers can apply their knowledge to real-world problems and improve their skills for interpreting and using stable isotopes in ecological research. This book is designed for students and scientists from different backgrounds who share the common interest in stable isotopes.