To a great extent, the behavior of nanoparticles is dominated by their surface properties. Particularly for the handling and application of nanoparticles in liquid dispersions and for the incorporation of nanoparticles into a matrix to form nanocomposites, the surface chemistry needs to be controlled and often adjusted. In many cases, high stability against agglomeration in aqueous or hydrophilic media can be reached via electrostatic stabilization. For most applications, however, organic ligands need to be coordinated to the particle surface to realize optimum compatibility with the surrounding medium and in some cases, also achieve additional functionality. Typically, this is achieved after the synthesis in a so-called post-synthetic modification step. Whilst a variety of strategies for such a modification have been developed in the past years that can be applied for nanoparticles of different kinds of materials fabricated via different routes, the reliable analysis of the surface chemistry remains a challenge in many cases. In particular, due to difficulties of separating nanoparticles from the liquid medium, the determination of bound vs. unbound ligand species, the particular mode of coordination to the nanoparticle surface, and a quantification of the bound ligands are tricky and require sophisticated strategies and advanced analytical techniques. In this contribution, a number of examples are presented for the precise characterization of the particle surface chemistry, including techniques that can be implemented in liquid dispersion, also enabling the determination of the affinity of ligands to the nanoparticle surface, as well as methods for nanoparticles in the dried state that are especially suited for quantitative analysis.