The negative numbers represent a central theme in the 7th grade curriculum that ought not to be reduced to the application of poorly-understood rules of calculation but rather should challenge and support the students/ forces for thinking and imagination. How can the concept of this new domain of numbers be provided with conceptual depth? Which attitudes and forces can be developed in the process? This exercise book for students contains a rich spectrum of the most diverse problems that on the one hand support in an exemplary way skill acquisition with respect to a variety of different thought forms concerning the application of negative numbers, while on the other hand continually stimulating self-reflection on the student's own activity. The teacher's book contains the solution to all exercises (including an explanation of the solution path), a didactic exposition of the theme, as well as hints for possible ways to organize the instruction (either as a main lesson or otherwise).