This book has some excellent ideas and design concepts for landscaping those hills of yours. For me, the diversity of colorful photos provided some wonderful ideas when working with my landscape architect. This book has a good section on erosion control and drainage, but probably not detailed enough for more severe grades - in which case you should probably consult a professional. We already hired a landscape architect, but having this book has given us some great ideas and direction for what we want to do with our hillside.
The other reason you may want a professional is that the last section which recommends plants to use for erosion control is not all that useful. In fact, I knocked a few stars from my review because they specifically recommended Hedera (English Ivy) and Hypericum (St. Johnswort) on their Ground Cover list. Both of these species are quite invasive and extremely bad selections, especially in the Pacific Northwest. In fact, Hedera is on our state's Noxious plants list and eradication of Ivy is a high priority. Additionally, some studies have shown that Ivy has little effect on erosion control. It is better to consult with your local nursery or landscape architect on best erosion control plants to use in your specific location as these can differ significantly by zone.