The heading of `environmental science' covers a broad range of topics, but some themes recur. Among these are the chemical complexity, inhomogeneity, dilution and non-ideality of materials. Hard X-ray XAFS techniques are well suited to application in this area because they are element-specific, have very lenient requirements on sample preparation, can be applied at many distance scales, can be used at low concentrations of a given element and do not require crystallinity. In this chapter, these general considerations will first be discussed. Then, because the field of environmental science is vast, a few illustrative examples, chosen to illustrate some of the directions in which the field has gone and some of the experimental considerations involved in using XAFS for environmental purposes, will be described. Some other areas in which XAFS has frequently been applied will then be briefly listed.