Potentiometric and calorimetric titrations are performed to study the complexation reactions of non-cyclic polyethers and crown ethers with Ag+ in acetone and propylene carbonate. With increasing chain length of the non-cyclic ligands the complex stability increases due to favourable enthalpic contributions. The macrocyclic polyethers already possess a preformed cavity for the complexation of the Ag+ ion. The cavity size and substituents influence the stability constants of the complexes formed. Only the smallest crown ether examined, 12-crown-4, forms 2:1 complexes in acetone and propylene carbonate solutions. The highest values of the stability constants for the reaction of Ag+ with crown ethers are measured if the dimensions of the silver ion and of the cavities are nearly identical. The results clearly demonstrate the entropic origin of the macrocyclic effect in both solvents.