A review is presented of the electrical characteristics of highdensity, high-performance interconnections used in digital and communication applications. These interconnections behave as lossy transmission lines for the frequency range of interest. A brief theoretical explanation of the key properties of lossy, coupled transmission lines is given. A new short-pulse propagation technique used for characterizing a large category of wiring is described. A detailed description is made of each of the major interconnect types encountered, namely, shielded cables, printed circuit boards, ceramic carriers, thin-film wiring, and on-chip wiring. Representative examples are given in each case to highlight the key performance-limiting parameters. The modeling and measurement techniques used are explained and examples are given. Future technological directions and their effect on performance are discussed.