This course has been concerned with the future of electronics, and especially digital electronics. At present digital electronics is dominated by a single architecture, Complementary Metal Oxide Semiconductor (CMOS), which is built on planar silicon field effect transistors. Steady improvements in the performance of CMOS circuits have been achieved by shrinking the feature sizes of the component transistors. This remarkable progress in electronics achieved over a period of > 30 years has come to underpin much of our economic life. In this section, we address both practical and thermodynamic limits to silicon CMOS electronics. It is likely that these limits will dominate the future of the electronics industry.