Earlier, chemists mainly focused on the reaction of molecules instead of the interaction of molecules. However, supramolecular chemists paid attention to the formation of molecular assemblies, which are held together by a range of relatively weak intermolecular interactions. In this chapter, an overview of the respective intermolecular interactions that may contribute to aggregation processes is presented, with emphasis on those aspects that appear of significance to a practicing supramolecular chemist. Each intermolecular interaction is examined through relevant examples as well as those that elucidate exciting aspects of the aggregation process or its possible applications. Remarkably, current trends in the field are also examined. Introduced in sections are ionic and molecular recognition, hydrogen bonds, halogen bond, electrostatic interactions, ionic and dipolar interactions, charge transfer interactions, coordination interactions, van der waals interactions, π- interactions, and hydrophobic effects. It gives many practical ideas for chemists dealing with the design of new host-guest systems; it is also necessary for understanding the structural interplays that control the assembly of known systems both in the solid-state and in solution. Finally, conclusions and future outlook are presented and discussed.