More than a century ago , electrical engineering was so much simpler. Basically, it referred to the technical end of telegraphy, trolley cars, or electric power. Nevertheless, here and there members of that fledgling profession were quietly setting the stage for an era in industrial history unparalleled for its innovation, growth, and complexity.

That decades-long saga was punctuated early on by spark-gap radios, tubes, and amplifiers. With World War II came radar, sonar, and the proximity fuze, followed by electronic computation. Then came solid-state transistors and integrated circuits: originally with a few transistors, lately with hundreds of millions. Oil-filled circuit breakers the size of a cottage eventually gave way to solid-state switches the size of a fist. From programs on punch cards, computer scientists progressed to programs that write programs that write programs, all stored on magnetic disks whose capacity has doubled every 15 months for the past 20 years [see " Through a Glass"]. In two or three generations, engineers took us from shouting into a hand-cranked box attached to a wall to swapping video clips over a device that fits in a shirt pocket.

Today, at its fringes, electrical engineering is blending with biology to establish such disciplines as biomedical engineering, bioinformatics, and even odd, nameless fields in which, for example, researchers are interfacing the human nervous system with electronic systems or striving to use bacteria to make electronic devices. On another frontier--one of many--EEs are joining forces with quantum physicists and materials scientists to establish entirely new branches of electronics based on the quantum mechanical property of spin, rather than the electromagnetic property of charge.

What EEs have accomplished is amazing by any standard. "Electrical engineers rule the world!" exclaims David Liddle, a partner in U.S. Venture Partners, a venture capital firm in Menlo Park, Calif. "Who's been more important? Who's made more of a difference?"

But as the purview of electrical engineering expands, does the entire discipline risk a kind of effacement by diffusion, like a photograph that has been enlarged so much that its subject is no longer recognizable? For those in the profession, and those at universities who teach its future practitioners, this is not an abstract issue. It calls into question the very essence of what it means to be an EE.

" I remember hearing the same sort of words 20 years ago," says Fawwaz T. Ulaby, professor of electrical engineering and computer science and vice president for research at the University of Michigan, in Ann Arbor. Indeed, two decades ago, in its 20th anniversary issue, IEEE Spectrum ran an article describing how the drive toward abstraction and computer simulation was reshaping electrical engineering [see "The Engineer's Job: It Moves Toward Abstraction," Spectrum, June 1984]. Breadboards and soldering irons were out; computer simulations and other abstractions were in.

If anything, the variety of things EEs do has actually increased since then. If you are an EE, you might design distribution substations for an electric utility or procure mobile communications systems for a package delivery company or plan the upgrade of sprawling computer infrastructures for a government agency. You might be a project manager who directs the work of others. You might review patents for an intellectual property firm, or analyze signal strength patterns in the coverage areas of a cellphone company. You might preside over a company as CEO, teach undergraduates at a university, or work at a venture capital or patent law firm.

Maybe you work on contract software in India, green laser diodes in Japan, or inertial guidance systems in Russia. Maybe, just maybe, you design digital or--more and more improbably--analog circuits for a living. Then there are the offshoots: field engineering, sales engineering, test engineering. Lots of folks in those fields consider themselves EEs, too. And why not? As William A. Wulf, president of the National Academy of Engineering (NAE), in Washington, D.C., notes, the boundaries between disciplines are a matter of human convenience, not natural law.

If your aim is to define the essence of the electrical engineering profession, you might ask what all these people have in common. Perhaps what links them is the connection, however indirect, between their livelihoods and the motion of electrons (or photons). But is such a link essential to defining an EE? Not to Ulaby.

"Engineers tend to be adaptive machines," he says. Even though there's little resemblance between the details of what he learned in school and the work he does now, Ulaby, who is also editor of the Proceedings of the IEEE , has no doubt that he himself is an EE.

David A. Mindell of the Massachusetts Institute of Technology, in Cambridge, says the perception that the field is heading toward unrecognizability is a constant. (This associate professor of the history of engineering and manufacturing also designs electronic subsystems for underwater vehicles.) Perhaps the biggest change to the electrical engineering field occurred in 1963, when engineers who worked with generators and transmission lines and engineers who worked with tubes and transistors finally agreed that they were all part of the same discipline.

That was the year the American Institute of Electrical Engineers (AIEE), whose membership consisted largely of power engineers, agreed to merge with the Institute of Radio Engineers (IRE) to form the IEEE. In the 1980s, jokers were already suggesting that the IEEE should become the Institute of Electrical Engineers and Everyone Else. Then, as now, many observers worried that such mainstay specialties of the profession as power engineering and analog circuit design were stagnating, while all of the interesting progress took place at the boundaries between electrical engineering and other fields.

Forced to choose a single core activity of electrical engineering, many technologists would probably pick circuit design, in all its various manifestations. It wouldn't be anything like a unanimous choice, of course, but it would make sense in much the same way as identifying surgery as the archetype of the medical profession, say, or litigation as the heart of lawyers' work. Circuit design is, after all, what non-EEs tend to associate with electrical engineering, if only in a vague way. And if a connection to moving electrons is a fundamental characteristic of an EE's occupation, then circuit designers must be counted among the elite.

By that standard, Tom Riordan is an EE's EE. Now a vice president and general manager of the microprocessor division at chip conglomerate PMC-Sierra Inc., in Santa Clara, Calif., Riordan started his career in the late 1970s, when circuit design was king and designing your own microprocessor, he says, "was the be-all and end-all" of an electrical engineering career. Riordan helped design a single-chip signal processor at Intel Corp. and created special-purpose arithmetic units at Weitek Corp. He then played a key role in developing the design for the central processing unit of the single-chip reduced instruction set computer (RISC) that made what was then MIPS Computer Systems Inc. a commercial success in the early 1990s.

That kind of deeply technical 14- to 16-hour-a-day work, mixing intimate knowledge of architectural principles with the intricacies of semiconductor layout required to get a chip working at speed, is what Riordan still thinks of as engineering. He designed a floating-point unit for MIPS and oversaw the architecture of a couple of more generations of CPUs before starting his own company, Quantum Effect Devices Inc., where he guided about a dozen engineers over the hurdles of creating MIPS-compatible custom processors. On the side, he negotiated with customers and dealt with investors and investment bankers.

After PMC-Sierra bought Quantum in 2000, Riordan dropped much of the CEO side of his job. This shift, he says, gives him roughly one day a week of what he calls "real engineering"--helping to make complex tradeoffs in CPU architecture or reviewing the niceties of yet another reduction in the size of a chip feature. He may not get into the same level of technical detail on every project as he once did, but he asserts that knowing the ins and outs of nanometer-scale circuit design is still part of his job.