The aim of this study is to outline the structure of a possible grammar of Oscar Niemeyer’s architectural language, focusing on the so-called “free forms.” The idea is to assess the extent to which it is possible to shed some light on the discussion of architectural freedom as used by many authors when describing the work of the Brazilian architect. The investigation associates geometric relations present in Niemeyer’s buildings to the Shape Grammar model as proposed by Stiny & Gips (1975). The model made possible the depiction of consistencies in vocabulary, rules and operations deployed by Niemeyer. This eventually led to the description of an original architectural language present in Niemeyer’s buildings.