This chapter shows that the importance of studying the organization of pure Ionic liquids (IL) and ILs in solution by reporting the results obtained from spectroscopic methods in this research area up until and the perspectives of the investigations. Several properties of ILs such as density, viscosity, polarity, and conductivity can be drastically changed by the presence of small amounts of other substances, and this may lead to significant modifications in, for example, the rate and selectivity of chemical reactions performed in their midst. The chapter provides a great deal of material to be covered, and it was necessary to make some limitations to the scope: Only ILs with heterocyclic cations were considered; only spectrometry methods, namely, mass spectrometry, nuclear magnetic resonance, light scattering, or photon correlation spectroscopy that consider the most important for IL aggregate detection. The chapter concludes with an optimistic view for the future expansion of the development of IL aggregates as a new soft material.