This chapter explores how to create valid, fair, and relevant assessments in multilingual teaching contexts. While the “perfect assessment” does not exist, the intention of all assessments should be to make them as fair as possible to all students, providing proof to what degree the desired learning outcomes have been attained, but also serving as an indicator of adjustments or support needed to help students develop as far as they can. In foreign language classrooms, language is usually both a target and a tool. In multilingual contexts among language learners, the language of instruction is undoubtedly a tool to communicate disciplinary content, but only sometimes a target in instruction. This chapter examines the distinction of content concerning language, using syllabi and assessment samples from the social and the natural sciences as well as English as a Foreign Language to compare the language skills needed in different disciplines. Data comes from research conducted in Sweden on teachers’ assessment practices in Content and Language Integrated Learning (CLIL) and English Medium Instruction (EMI) among newly arrived immigrant students. The chapter presents how to design valid and fair assessments among language learners, taking both students’ needs and the intended learning outcomes (ILOs) into account. Assessment validity theory and an extended version of constructive alignment are used as a theoretical framework. Validity is discussed in relation to the alignment of ILOs, teaching, and assessment, as well as how language and feedback are integrated into course design. For the comparison of syllabi, the Common European Framework of Reference for Languages (CEFR) and Anderson and Krathwohl’s description of knowledge dimensions and cognitive processes serve as references. The chapter describes how the student’s language proficiency and target language outcome should be considered and integrated into the assessment process before, during, and after the assessment. This is a necessary procedure in subject content courses and foreign language classrooms since it is only possible to learn a language with content to write or talk about or content with the necessary language skills. Content and language are inextricably connected and interdependent, whether it be a matter of individual teachers’ work or cross-disciplinary collaboration.