**4. Conclusions**

General aspects of Small Angle X-Ray applied to the study of colloidal particles in solution were presented. Two examples of application were shown, demonstrating the versatility of the SAXS technique. One of the main strengths of this technique is the possibility of investigate systems directly in solution, close to the native state, in a broad range of sizes and molecular weights. On the other hand, due to the low information content of a typical SAXS data, the scattering data has to be correlated and supported by additional information, obtained from other experimental techniques. In this way, even thought SAXS data can provide a valuable and important structural information, the technique and the modeling methods has to be applied with extreme precaution and always cross checked with several additional results in order to provide relevant, unambiguous information and, most importantly, avoid wrong data interpretation. As shown in this chapter, absolute scale calibration and the comparison of hydrodynamic properties of the obtained models with the ones obtained experimentally are two very useful tools for results checking and model validation.
