The present thesis focuses on particle aggregation in aqueous media, particularly on the role of different ions in solution. I present a rather wide view of this topic, starting with the well researched question of multivalent ions and the Schulze-Hardy rule, continuing with the less investigated effects different types of monovalent ions and the Hofmeister series, and finally addressing an entirely unexplored field, namely particle aggregation in water-miscible ionic liquids. This thesis describes a broad view of particle aggregation in different ionic media and presents a wealth of original results. Two among those should be particularly stressed. First, the presented comparison between light scattering and direct force measurements represents a novel approach to study particle aggregation phenomena. Second, the investigations involving ILs are innovative and will surely influence the rapidly evolving field of ILs in the near future. Therefore, the originality of this thesis is substantial.