This study examined the changes that a group of nine Israeli 7th grade mathematics teachers, who collaborated on editing the textbook they used in class, chose to make in the textbook. Data sources included the project website (using a modified wiki-book platform), the group meetings, interviews with the teachers, individual papers written by the teachers, and a research journal. Data analysis revealed 4 types of change that the teachers wittingly and purposely suggested making. Three of them comprised changes related to ways suggested in the textbook to teaching and learning mathematical content: integrating technological tools, re-structuring textbook content presentation, and adding materials for students with low achievements. The 4th type of change was of a different nature, associated with creating organizing tools embedded in the textbook in order to make the textbook user-friendlier. The work on the 4 types of change involved 3 kinds of challenge: professional, conceptual, and technical.