Here is a brief excerpt from a classic essay by Daniel Goleman that has been reprinted by Harvard Business Review. To read the complete article, check out the wealth of free resources, obtain subscription information, and receive HBR email alerts, please click here.

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It was Daniel Goleman who first brought the term “emotional intelligence” to a wide audience with his 1995 book of that name, and it was Goleman who first applied the concept to business with his 1998 HBR article, reprinted here. In his research at nearly 200 large, global companies, Goleman found that while the qualities traditionally associated with leadership—such as intelligence, toughness, determination, and vision—are required for success, they are insufficient. Truly effective leaders are also distinguished by a high degree of emotional intelligence, which includes self-awareness, self-regulation, motivation, empathy, and social skill.

These qualities may sound “soft” and unbusinesslike, but Goleman found direct ties between emotional intelligence and measurable business results. While emotional intelligence’s relevance to business has continued to spark debate over the past six years, Goleman’s article remains the definitive reference on the subject, with a description of each component of emotional intelligence and a detailed discussion of how to recognize it in potential leaders, how and why it connects to performance, and how it can be learned.

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Every businessperson knows a story about a highly intelligent, highly skilled executive who was promoted into a leadership position only to fail at the job. And they also know a story about someone with solid—but not extraordinary—intellectual abilities and technical skills who was promoted into a similar position and then soared.

Such anecdotes support the widespread belief that identifying individuals with the “right stuff” to be leaders is more art than science. After all, the personal styles of superb leaders vary: Some leaders are subdued and analytical; others shout their manifestos from the mountaintops. And just as important, different situations call for different types of leadership. Most mergers need a sensitive negotiator at the helm, whereas many turnarounds require a more forceful authority.

I have found, however, that the most effective leaders are alike in one crucial way: They all have a high degree of what has come to be known as emotional intelligence. It’s not that IQ and technical skills are irrelevant. They do matter, but mainly as “threshold capabilities”; that is, they are the entry-level requirements for executive positions. But my research, along with other recent studies, clearly shows that emotional intelligence is the sine qua non of leadership. Without it, a person can have the best training in the world, an incisive, analytical mind, and an endless supply of smart ideas, but he still won’t make a great leader.

In the course of the past year, my colleagues and I have focused on how emotional intelligence operates at work. We have examined the relationship between emotional intelligence and effective performance, especially in leaders. And we have observed how emotional intelligence shows itself on the job. How can you tell if someone has high emotional intelligence, for example, and how can you recognize it in yourself? In the following pages, we’ll explore these questions, taking each of the components of emotional intelligence—self-awareness, self-regulation, motivation, empathy, and social skill—in turn.

Evaluating Emotional Intelligence

Most large companies today have employed trained psychologists to develop what are known as “competency models” to aid them in identifying, training, and promoting likely stars in the leadership firmament. The psychologists have also developed such models for lower-level positions. And in recent years, I have analyzed competency models from 188 companies, most of which were large and global and included the likes of Lucent Technologies, British Airways, and Credit Suisse.

In carrying out this work, my objective was to determine which personal capabilities drove outstanding performance within these organizations, and to what degree they did so. I grouped capabilities into three categories: purely technical skills like accounting and business planning; cognitive abilities like analytical reasoning; and competencies demonstrating emotional intelligence, such as the ability to work with others and effectiveness in leading change.

To create some of the competency models, psychologists asked senior managers at the companies to identify the capabilities that typified the organization’s most outstanding leaders. To create other models, the psychologists used objective criteria, such as a division’s profitability, to differentiate the star performers at senior levels within their organizations from the average ones. Those individuals were then extensively interviewed and tested, and their capabilities were compared. This process resulted in the creation of lists of ingredients for highly effective leaders. The lists ranged in length from seven to 15 items and included such ingredients as initiative and strategic vision.

When I analyzed all this data, I found dramatic results. To be sure, intellect was a driver of outstanding performance. Cognitive skills such as big-picture thinking and long-term vision were particularly important. But when I calculated the ratio of technical skills, IQ, and emotional intelligence as ingredients of excellent performance, emotional intelligence proved to be twice as important as the others for jobs at all levels.

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Here is a direct link to the complete article.

Daniel Goleman is the author of international bestsellers, Emotional Intelligence, Working with Emotional Intelligence, and Social Intelligence, and the co-author of the acclaimed business bestseller Primal Leadership. He was a science reporter for the New York Times, was twice nominated for the Pulitzer Prize, and received the American Psychological Association’s Lifetime Achievement Award for his media writing. He lives in the Berkshires.