The primary aim of the thesis is to explain informality with the help of labor market segmentation theory in the case of Turkey. In so doing, the informalization process in Turkey is discussed with reference to not only the definitional confusions in different conceptualizations of the informal sector in the literature, but also trade liberalization, privatization, subcontracting relationships and the notion of &ldquo / flexible firm&rdquo / , as well. In order to find an answer to the question of &ldquo / how the dimensions of informality fit into the perception about labor market segmentation theory&rdquo / , the field surveys conducted by different authors are analyzed. The findings of these field surveys confirm a possible explanation of informalization via labor market segmentation theory in Turkey.