Selectively functionalized calix[4]arenes are used to build effective receptors for cations, anions and neutral molecules or for a combination of a cation and an anion. This was done by combination with a terphenyl unit (cation receptor), a uranyl-containing salen moiety (for anionic and neutral guests) or by introduction of sulfonamide groups (anion receptor). Conformational control is effected using the appropriate conditions for the lower rim alkylation, but the conformation can also be influenced by hydrogen bonding. New routes for the synthesis of selectively functionalized calix[4]arenes bearing a combination of functional groups at the upper rim were developed together with a simple method for the direct introduction of meta substituents. Nitrated calix[4]arenes have very good non-linear optical characteristics. Selective methylation and phosphorylation of p-tert-butylcalix[6]arene is shown to be possible when specific conditions are used. The conformational properties of selectively functionalized calix[6]arenes were studied by 1H NMR spectroscopy. The controlled conformation of 1,3,5-trimethoxy-p-tert-butylcalix[6]arene was used to synthesize a cryptocalix[6]arene.