The topic of bipolar compatible CMOS (BiCMOS) is a fascinating one and of ever-growing practical importance. The "technology pendulum" has swung from the two extremes of preeminence of bipolar in the 1950s and 60s to the apparent endless horizons for VLSI NMOS technology during the 1970s and 80s. Yet starting in the 1980s severallimits were clouding the horizon for pure NMOS technology. CMOS reemerged as a· viable high density, high performance technology. Similarly by the mid 1980s scaled bipolar devices had not only demonstrated new high speed records, but early versions of mixed bipolar/CMOS technology were being produced. Hence the paradigm of either high density . Q[ high speed was metamorphasizing into an opportunity for both speed and density via a BiCMOS approach. Now as we approach the 1990s there have been a number of practical demonstrations of BiCMOS both for memory and logic applications and I expect the trend to escalate over the next decade. This book makes a timely contribution to the field of BiCMOS technology and circuit development. The evolution is now indeed rapid so that it is difficult to make such a book exhaustive of current developments. Probably equally difficult is the fact that the new technology opens a range of novel circuit opportunities that are as yet only formative in their development. Given these obstacles it is a herculean task to try to assemble a book on BiCMOS.