Rationalism is a creative method that has accompanied architecture since its earliest beginnings. In Bulgaria, this is very clearly evident in the architecture of the folk masters from our early Renaissance period. In the contradictory development of European architecture, it has repeatedly had to give way to stylistic trends subject to formalistic enthusiasms. Architects of the 19th century went particularly far in this direction, but at the same time the first theoretical precursors of 20th-century rationalism appeared. (Zemper, Sullivan, etc.). Attempts to conduct a multifaceted analysis of the contribution of rationalism to the development of contemporary architecture have revealed a series of its positive and negative effects.