In this chapter, we will combine some of ideas that have been developed earlier to describe the total interaction between a solid body and a fluid flowing through it or around it. The chapter title, “Viscous Flow,” correctly implies that we will be considering viscous effects in contrast to the analysis of inviscid flow, which is a subject of particular interest to aerospace engineers. The subject of inviscid flow tends to be quite sophisticated mathematically and is beyond the scope of this book.