The purpose of this article is to describe the use of different techniques, such as dynamic light scattering (DLS), electron microscopy (EM), and atomic force microscopy (AFM), on the characterization of particulate systems. A brief theoretical introduction for each technique is presented, including advantages and disadvantages. Micro- and nanoparticles of polyurethane were used as examples to illustrate the use of these techniques. Using the techniques of electron microscopy we were able to obtain three-dimensional images revealing the size and morphology of micro- and nanoparticles. In relation to the size of the particles, different results were observed when the techniques of DLS and AFM were used and compared. The results were discussed, taking into account the measuring principle inherent to each technique.