water resulting in rapid decomposition, [12] making processing of the material challenging and resulting in detrimental effects on its optical and electronic properties. [13] The ambient degradation of BP presents a significant hurdle to realizing the full potential of BP in various applications. The successful application of BP will rely either on its exclusion from the factors that contribute to its degradation or protection methods that prevent its degradation in ambient conditions. Literature reports that have studied the degradation chemistry of BP have revealed some conflicting results regarding the effect of water, oxygen and light, indicating that BP has a complex surface chemistry. The indepth characterization of BP degradation is critical for the development of new protection strategies and progress of the material and its applications. The role of the surface oxide as a passivation layer that stabilizes BP has also created some debate between researchers. Although a stabilizing oxide has been reported in theoretical studies, [14] experimental reports question the challenges of creating a self-limiting surface oxide on BP. [15] Protection of BP can also be accomplished by capping layers, [13c,16] functionalization, [17] solvent passivation, [10b] or the incorporation of polymers. [18] Ambient degradation can be suppressed by covalent functionalization where chemical binding of molecules to the reactive lone pairs on the surface prevent decomposition. [17] Noncovalent functionalization can also be employed, which inhibits degradation by passivating BP nanoflakes through noncovalent interactions. [17b] Solvent passivation forms a protective barrier against oxidants while polymer coatings, or the formation of BP-polymer hybrids enhances its oxidation resistance while also modifying its properties. This review outlines the factors that influence the oxidation of BP from a surface chemistry perspective, including the effect of water, oxygen, and light on the degradation of BP, as well as elucidation of the oxidation mechanism through analysis of BP exposed to single oxidants and evaluation of the oxidation products. Additionally, an overview of current advances in the protection strategies for BP is presented. 2. Structure, Properties, and Exfoliation of BP BP has an orthorhombic crystal structure and consists of layers of phosphorene held together by van der Waals interactions, as depicted in Figure 1a. [19] The individual layers of phosphorene consist of phosphorus atoms covalently bound Exfoliation of black phosphorus (BP) into phosphorene has led to the discovery of its semiconducting properties and tunable bandgap, enabling its use in a range of applications including transistors, batteries, and sensors. However, BP's ambient instability poses a considerable challenge to its incorporation into functional devices. Observed changes to the surface chemistry of BP during degradation has recently provided insight into the degradation pathways. In this review, degradation mechanisms are discussed including th...