There is international interest today in the fate and transformation of phosphorus (P) applied to soils due to historical overapplication of P from organic wastes. This overapplication has increased soil solution P concentrations and enriched the erodible fraction of soil with P. This is of major concern as significant water quality deterioration can occur if P applied to soils in organic wastes reaches water bodies. Just as the bioavailability of P compounds depends upon their chemical form, it is becoming increasingly apparent that information about different forms of P is needed for holistic management of organic wastes. A number of chemical and biological methods have been employed to partition total P into more specific chemical forms in organic wastes. However, there has been no previous effort to review and synthesize the literature and to critically analyze the various techniques with promise for chemical speciation of P in organic wastes. In this chapter, we review various types of organic wastes and factors affecting P composition in organic wastes, from production to land disposal. Then, we discuss the various methods that have been used to characterize P forms, including water extractable P (WEP) physicochemical fractionation, sequential chemical fractionation, enzymatic hydrolysis, nuclear magnetic resonance (NMR), and x-ray absorption near edge structure (XANES) spectroscopy. To summarize the conclusions, WEP is quick chemical test that should be employed to determine the readily dissolved P in organic wastes and to assess the potential risk of wastes on water quality. The potential bioavailability of P forms in the liquid wastes can be similarly assessed by a rapid and low cost physicochemical fractionation method. Enzymatic hydrolysis and solution state NMR can be of great benefit to characterize organic P species in wastes, whereas solid-state NMR and XANES spectroscopy are better suited to study the inorganic P minerals in the wastes. NMR and XANES methods are both quantitative and can be used to study the influence of management practices on P speciation. Solid-state NMR and XANES methods are capable of performing analysis of heterogeneous material and provides complementary information about P compounds in organic wastes. The combined use of sequential chemical fractionation and spectroscopic methods (NMR, XANES) allows for accurate identification of P compounds in the sequential extracts. Case studies are included throughout the chapter to discuss wider applicability of a particular method. We conclude this chapter by suggesting that more than one method may be necessary for complete determination of P species in organic wastes.