It is essential for students to think clearly about fundamental biological concepts. One of the benefits of writing is that it promotes and enhances thinking. If students can write clearly, they are thinking clearly. Writing helps to connect new knowledge with prior knowledge and promotes the construction of knowledge. Writing-to-learn activities enhance vocabulary development, promote ownership, and invite participation by a broader range of students, particularly females and minority students. One writing-to-learn activity that is proving successful in high school classes is writing "how-to" books. A how-to book describes a process and explains how to do a variety of tasks, such as starting an insect collection, classifying trees, dissecting a cat, using a compound microscope, or separating DNA using gel electrophoresis. How-to books make learning relevant, promote retention, and are student-driven learning. The purpose of this paper is to describe a how-to book assignment in ecology and horticulture high school classes, offer instructional tips, provide student comments about the assignment, and offer a list of student-made how-to book titles. (Contains 3 figures.)