This open access book distinguished itself from other publications by offering step-by-step instructions on how to extract, purify, provide modifications, and major issues to be encountered during the process. For the δ¹⁸OP method to progress, further fundamental research as well as field and laboratory studies need to be conducted for a better understanding of P cycling in the environment.  Chapter 1 outlines the background and examples of δ¹⁸Op studies in sediments, soils, fresh water, mineral fertilizers, and plants. Chapters 2 and 3 examine the stepwise extraction and purification protocols including reagents, equipment and consumables and preparations for analyses. Chapter 4 examines some of the challenges and modifications during the purification process. Chapter 5 discusses planning and designing of a study using δ¹⁸Op, external quality assurance with an example of an inter-laboratory study. Chapter 6 outlines the conclusions, future trends, and opportunities, the scaling out of the method from laboratory to field studies.  It is expected that the δ¹⁸O_P would be extensively applied in research geared to understand phosphorus dynamics in different agro-environments.