This study analyzed the integration of crosscutting concepts in the teaching of English language in Tanzania secondary schools. The education policy in Tanzania since 2014 recommends the integration of crosscutting concepts at all levels of education. The teaching of English language curriculum however, is a contested issue, which continues to raise concerns and bitter debates questioning its singular curriculum soundness and appropriateness of its content for the subject, which is flexible to allow integration of crosscutting concepts from various disciplines. This study adopted an exploratory sequential mixed-methods design where both qualitative and quantitative data were collected and analyzed sequentially. This study was guided by Cummins theory of second language teaching. Data was collected by means of document analysis, questionnaires, and Focus Group Discussion (FGD) and analyzed using descriptive statistics, Mann-Whitney U test, Pearson product-moment correlation coefficient, multiple regression analysis, and content analysis. Research participants include 92 teachers of English and 458 form one students from 9 randomly sampled schools. The findings of this study revealed that although crosscutting concepts are not entirely lacking from textbooks, syllabus, and students’ exercise books, they are not well and comprehensively integrated. The extent of integration of crosscutting concepts in English language teaching is moderate, among other findings. The outcome of the findings of the study is an interdisciplinary curriculum model which if implemented would improve the integration of crosscutting concepts in the teaching of English language in secondary schools in Tanzania. The study recommends that the English interdisciplinary curriculum model developed in this study be used to achieve effective integration of crosscutting concepts in the teaching of English language to secondary schools in Tanzania.