Book excerpt: Text readability is at the core of successful reading instruction and language learning. To counteract the challenges of complex reading content, text leveling is a vital necessity for readers with limited language access. A transdisciplinary analysis of reading development and linguistic interrelations builds the theoretical foundation of the base-1 method. This method focuses solely on structural and functional text elements on the word, sentence and cohesion level. But this book also discusses the significance of other prevalent readability factors, such as the reader ́s language knowledge or socio-cultural background. The base-1 method is designed to level early reading texts in German and other alphabetic languages. Experimental tests with a German immersion population has led to a preliminary calibration to demonstrate the validity of this approach. Bernd Nuss ist erfahrener Immersionslehrer in verschiedenen Programmen, die sich über Nord-, Zentral- und Südamerika erstrecken. An der E. E. Waddell Language Academy wirkt er schulintern als Immersion Facilitator, kooperiert mit Bildungsorganisationen und betreut die Praktika von Gaststudierenden an der Schule. Bernd Nuss has worked as an educator and facilitator in English and German language immersion programs all over the Americas and in Europe. In this capacity, he has also been collaborating as a researcher with universities and other educational institutions in Europe, Asia, and the USA.