The new Lewis acid Al(OTeF₅)₃ and its acetonitrile adduct CH₃CN→Al(OTeF₅)₃ were obtained by a simple one‐step synthesis in batches of up to 15 g. Al(OTeF₅)₃ and the adduct were characterized by vibrational spectroscopy (IR, Raman) and quantum‐chemical calculations. Furthermore, five different salts of the new weakly coordinating anion [Al(OTeF₅)₄]⁻ were prepared in a two‐step procedure. [Ph₄P][Al(OTeF₅)₄], Cs[Al(OTeF₅)₄], [Ph₃C][Al(OTeF₅)₄], as well as the protonated benzene derivatives [C₉H₁₃][Al(OTeF₅)₄] and [C₆H₇][Al(OTeF₅)₄] were characterized by low‐temperature single‐crystal X‐ray diffraction and NMR spectroscopy. Arenium salts have rarely been characterized in the solid state and were synthesized in this work in a simplified fashion.