The unification of alphabets should be considered as the most exciting initiative of the whole language building [jazykovoe stroitel’stvo] in the Soviet Union in the early 1930’s. My paper aims at exploring the scopes and the results of this project, as well as its internal logics. I will try to examine how linguistic politics could be explained in the frame of phonological theory, which anticipated Troubetzkoy’s reflections by about fifteen years. Then I will show how concretely the unified alphabet was elaborated, and for which languages, among the Caucasian, Turkic and others. I will explain how the new alphabet was received by national elites and by politicians, and, finally, analyse the reasons for its failure. In the light of my analysis, the passage to Cyrillic scripts in the late 1930’s appears not only as a political, but also a scientific issue.