In this compilation licentiate thesis, two studies, concerned with genre and genre-based writing, are synthesized and discussed. Genres are often used as a pedagogical device for teaching the writing of educationally valued texts. The focus is on what is here termed genre metastability, a conceptual tool for understanding how these genres can appear both as fixed and as flexible, that is, offering both constraints and creativity for writing. The findings, based on a case study into genre-based history instruction, show how these, ostensibly opposing aspects, coexist in teaching and that they can be productively put to use by teachers as a means of differentiating instruction. Further, the thesis explores how the fixed/flexible dynamic can be used as a tool for understanding how similar types of history texts can offer diametrically opposed historical understanding of content. These findings have implications for teachers, teacher educators, and (history) textbooks in terms of a deepened understanding of how, or rather when, genres constrain, and when they foster creativity.