The formation and characterization of molecular capsules resulting from the self-assembly between oppositely charged (thia)calixarenes in polar solvents like MeOH and MeOH–H2O are reported. The multiple ionic interactions allow the self-assembly of the complementary (thia)calixarenes 1 and 2a–d into 11 complexes as revealed by 1H NMR and mass spectrometry (ESI-MS). Isothermal titration calorimetry (ITC) was used to determine the association constants, which, depending on the ionic groups involved in the complexes, vary between 103 and 106 M–1. An X-ray structure of the assembly 1 2d was also obtained. Unlike in solution, in the solid state 1 2d forms a 11 three-dimensional network in which 2d adopts a 1,2-alternate conformation.