This lecture covers the principles of supramolecular chemistry, focusing on crown ethers and their complexation with alkali metal ions. Topics include solvation enthalpy, accidental synthesis, extraction methods, host-guest interactions, sandwich complexes, and applications in phase transfer catalysis and anion activation. The lecture also discusses the complexation of ammonium ions, heterocrowns, podands, the macrocyclic effect, lariat ethers, cryptands, and the importance of preorganization in cation binding. Additionally, it explores chromo-ionophores, cation recognition by fluorescence, redox-responsive ionophores, and anion recognition considerations. Examples of fluorescence sensors, redox-responsive ionophores, and protein binding to anions are presented, along with the design of receptors for carboxylic acids.