The characterization of the solid phase is one of the first steps in the study of any of the myriad of environmental reactions that involve solids and solid-liquid interfaces. Environmental solids range from relatively pure and crystalline phases to heterogeneous and multiphasic particle aggregates whose characterization requires a combination of a number of analytical methods and methodologies. The first section of this paper gives a cross section of general strategies used in different departments at EAWAG for the characterization of field samples of both natural and anthropogenic origin. The morphological characterization and the determination of the chemical composition is described in respect to the properties of anthropogenic solids. As an example, the long-term behavior of incinerator bottom ash is discussed in a case study. A second section gives two examples of molecular level studies on environmental solids: application of Extended X-Ray Absorption Fine Structure (EXAFS) spectroscopy for the characterization of poorly crystallized manganese lake particles in the context of the genesis of lake sediments, and in situ Atomic Force Microscopy (AFM) and Fourier Transform Infrared (FTIR) studies on synthetic goethite particles during the oxidation of FeII and the reduction of CrVI.