EPHEMERAL. To survive and thrive in this century, managers will need to hard-wire a new set of rules and guideposts into their brains. Not so long ago, for example, leaders believed that building assets over the long haul guaranteed competitive advantage. In this new century, success will go to the companies that partner their way to a new future, not those that put heavy assets onto their balance sheets. Leaders once thought that creating intense rivalries among competitors motivated their employees and assured success. But in the days to come, a company's fiercest competitor might also be its most important collaborator. Since the dawn of trade, every business leader has wanted to build an enduring enterprise. In the new century, though, many companies will be intentionally ephemeral, formed to create new technologies or products only to be absorbed by sponsor companies when their missions are accomplished.

Many factors, from the need to expand beyond national borders to the inexorable shift toward intellectual capital, are driving change, but none is more important than the rise of Internet technologies. Like the steam engine or the assembly line, the Net has already become an advance with revolutionary consequences, most of which we have only begun to feel.

The Net gives everyone in the organization, from the lowliest clerk to the chairman of the board, the ability to access a mind-boggling array of information--instantaneously, from anywhere. Instead of seeping out over months or years, ideas can be zapped around the globe in the blink of an eye. That means that the 21st century corporation must adapt itself to management via the Web. It must be predicated on constant change, not stability, organized around networks, not rigid hierarchies, built on shifting partnerships and alliances, not self-sufficiency, and constructed on technological advantages, not bricks and mortar. Already, old business models that emphasized fixed assets, working capital, and economies of scale have become increasingly vulnerable to nimbler organizations that employ new technologies to reduce costs.

Leading-edge technology will enable workers on the bottom rungs of the organization to seize opportunity as it arises. Employees will increasingly feel the pressure to get breakthrough ideas to market first. Thus, the corporation will need to nurture an array of formal and informal networks to ensure that these ideas can speed into development. In the near future, companies will call on outside contractors to assemble teams of designers, prototype producers, manufacturers, and distributors to get the job done. Emerging technologies will allow employees and freelancers anywhere in the world to converse in numerous languages online without the need for a translator. ''The gap between what we can imagine and what we can achieve has never been smaller,'' says Gary Hamel, a consultant and author of Leading the Revolution.

That rapid flow of information will permeate the organization. Orders will be fulfilled electronically without a single phone call or piece of paper. The ''virtual financial close'' will put real-time sales and profit figures at every manager's fingertips via the click of a wireless phone or a spoken command to a computer. ''We don't have science-fiction writers who have seen and written this future,'' says Lowell Bryan, a consultant who leads McKinsey & Co.'s Global New Economy practice. ''Everything we see leads to greater diversity, greater choice, a far more integrative economy, yet more individualism.''

How, exactly, will these forces reshape the 21st century corporation? The organizations that flourish will have several defining features.

-- It's management by Web. That means not just Web as in Internet but the web-like shape of successful organizations in the future. If there are a pair of images that symbolize the vast changes at work, they are the pyramid and the web. The organizational chart of large-scale enterprise had long been defined as a pyramid of ever-shrinking layers leading to an omnipotent CEO at its apex. The 21st century corporation, in contrast, is far more likely to look like a web: a flat, intricately woven form that links partners, employees, external contractors, suppliers, and customers in various collaborations. The players will grow more and more interdependent. Fewer companies will try to master all the disciplines necessary to produce and market their goods but will instead outsource skills--from research and development to manufacturing--to outsiders who can perform those functions with greater efficiency.

Managing this intricate network of partners, spin-off enterprises, contractors, and freelancers will be as important as managing internal operations. Indeed, it will be hard to tell the difference. All of these constituents will be directly linked in ways that will make it nearly impossible for outsiders to know where an individual firm begins and where it ends. ''Companies will be much more molecular and fluid,'' predicts Don Tapscott, co-author of Digital Capital. ''They will be autonomous business units connected not necessarily by a big building but across geographies all based on networks. The boundaries of the firm will be not only fluid or blurred but in some cases hard to define.''

-- It's more about bits, less about atoms. The most profitable enterprises will manage bits, or information, instead of focusing solely on managing atoms (the corporation's physical assets). Sheer size will no longer be the hallmark of success; instead, the market will prize the ability to efficiently deploy assets. Good bit management can allow an upstart to beat an established player; it can also give an incumbent vast advantages. By using information to manage themselves and better serve their customers, companies will be able to do things cheaper, faster, and with far less waste.

-- It's mass customization. The previous 100 years were marked by mass production and mass consumption. Companies sought economies of scale to build large factories that produced cookie-cutter products, which they then sold to the largest numbers of people in as many markets as possible. The company of the future will tailor its products to each individual by turning customers into partners and giving them the technology to design and demand exactly what they want. Mass customization will result in waves of individualized products and services, as well as huge savings for companies, which will no longer have to guess what and how much customers want.

-- It's dependent on intellectual capital. The advantage of bringing breakthrough products to market first will be shorter-lived than ever, because technology will let competitors match or exceed them almost instantly. To keep ahead of the steep new-product curve, it will be crucial for businesses to attract and retain the best thinkers. Companies will need to build a deep reservoir of talent--including both employees and free agents--to succeed in this new era. But attracting and retaining an elite workforce will require more than huge paychecks. Corporations will need to create the kind of cultures and reward systems that keep the best minds engaged. The old command-and-control hierarchies, with their civil-service-like wages, are fast crumbling in favor of organizations that empower vast numbers of people and reward the best of them as if they were owners of the enterprise.

-- It's about speed. All this work will be done in an instant. ''The Internet is a tool, and the biggest impact of that tool is speed,'' says Andrew S. Grove, chairman of Intel Corp. (INTC) ''The speed of actions, the speed of deliberations, and the speed of information has increased, and it will continue to increase.'' That means the old, process-oriented corporation must radically revamp. With everything from product cycles to employee turnover on fast-forward, there is simply not enough time for deliberation or bureaucracy.

The 21st century corporation will not have one ideal form. Some will be completely virtual, wholly dependent on a network of suppliers, manufacturers, and distributors for their survival. Others, less so. Some of the most successful companies will be very small and very specialized; others will be gargantuan in size, scope, and complexity.

Some enterprises will last no longer than the time it takes for a new product or technology to reach the market. Once it does, these temporary organizations will pass their innovations on to host companies that can leverage them more quickly and at less expense. The reason: Every company has capabilities, but also disabilities, as Harvard Business School's Clayton M. Christensen puts it. The disabilities--things like deeply held beliefs, rituals, and traditions--often smother radical thinking. Some biotech upstarts, for example, have already served as external labs for large, powerful pharmaceutical companies. Some technology ventures have drawn seed capital from Cisco Systems Inc. (CSCO), only to be acquired by the network giant once the technology has been proven.