The mathe.delta Hessen G9 series precisely implements the requirements of the Hessian core curriculum 2011 for G9 (grammar schools and comprehensive schools). The series offers optimal materials for contemporary mathematics instruction: explicit references to the competencies and content being taught, competency-oriented self-tests, a high-quality range of tasks at various clearly marked levels of difficulty, a careful progression in the difficulty of the tasks, a clear structure through the double-page principle, motivating and student-friendly design, age-appropriate presentation of content, as well as tasks for differentiation and basic knowledge consolidation.