This volume has emerged from the evaluation of the German-English programs at secondary schools in Berlin (acronym: DEZIBEL). It begins with a theoretical justification for education and a curricular differentiation of bilingual subject teaching, describing the dimensions of competence acquisition in this form of instruction. The initial situation of the school trial is comprehensively documented, including the socioeconomic background and subjective well-being of the students, as well as the perspectives of the teachers. Both the English language competencies and the subject-related discourse competencies of the participants are assessed using highly differentiated test batteries and quantitatively analyzed, following the design of a comparative study (i.e., the performance of students in regular classes is continuously compared with that of students in bilingual programs). The volume concludes with detailed considerations for the further development of bilingual instruction, providing differentiated recommendations for accompanying English lessons and outlining the contours of an integrated bilingual didactics.