Editor's Note: This article is the first part of an three-part, exclusive, RainToday series based on Andrew's new book, All for One: 10 Strategies for Building Trusted Client Partnerships.

Some firms call them "office of the chairman" accounts, while others simply refer to them as key clients. These are the flagship client relationships that propel your growth in good times and provide essential ballast in a downturn. They are broad and deep, transcending any one individual professional or service offering. Usually, they endure for years.

These trusted partnerships account for a disproportionate share of most firms' revenues, profits, and intellectual capital. An archetypical example is Booz Allen Hamilton's 70-year continuous relationship with the U.S. Navy—truly a client for life.

Everyone would like to have more of these long-term, institutional relationships—but what roadmap should you follow? During the research for my new book All for One, I studied over 50 flagship client relationships in an effort to determine how, precisely, great service firms consistently build and sustain such enduring client relationships. I wanted to know: What strategies do they use? Why do some client relationships grow, while others fade away? How do they turn individual relationships into institutional ones? What kind of organizational culture do they develop to support these giant "redwoods" that are seemingly impervious to storms and disease?

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