In most schools of engineering, this is among the first interdisciplinary courses that third-year undergraduate students are likely to attend. This presents formidable challenges because any discussion of diffusion phenomena draws heavily on prior knowledge of physics, chemistry, and mathematics. In our traditionally inadequate way of teaching, these disciplines are presented as self-contained, autonomous units. Yet it should be the purpose of any instructor of diffusion theory and practice to show how they may be integrated. Heuristic arguments are certainly appealing — thus recommended — but the methods and tools to be developed must be robust enough to not immediately crumble with use. In that connection, attention to a known and consistent notation is vital. Furthermore, one cannot expect these students to be fully familiar with partial differential equations, and yet, that’s the very nature of the diffusion equation. Its properties must be explained. Finally, diffusion in solids suffers from a bewildering variety of “diffusion coefficients." These must be carefully defined and distinguished. A version of my class-notes will be included in my web-site within a few weeks (just type my name in Google). You are most welcome.