Generations are defined by the core values they carry for a lifetime, according to Chuck Underwood, founder and principal of Generational Imperative Inc., a Miamisburg, Ohio-based consultancy. The youngest people now flowing into the workforce are first-wave Millennials, aged 18 to 29 years old. Some demographers set the start of this generation slightly earlier, but there is broad agreement on who the Millennials are, what makes them tick and why managers and colleagues should care.

“New generations begin when there’s a significant change in the times they’re going to experience in their youth or the values they develop,” says Underwood. The values of the dominant generation in the workplace become the values of the leaders guiding the nation. The attitudes, beliefs, interests and styles of the 25-year-old Millennials today are a strong predictor of the nation’s direction.

Millennials should be recruited, trained, managed and promoted differently with respect for who they are. Further, different incentives will be needed to retain them. The firms recognizing this will attract the best, Underwood says.

Millennials were born at an average rate of about four million a year; this rate is equal to the rate of the huge baby-boomer generation, born between 1946 and 1964, but perhaps continuing longer—the end has not yet been determined. Underwood holds that membership in a generation is not confirmed until children reach 18 and societal core values are unchanged.

Both the boomers and the Millennials are much larger than Gen X, born between 1965 and 1981; but all are making distinct contributions, shaped by their values. Boomers are change agents, X-ers excel at innovation, and Millennials promise to be terrific employees and people leaders, but they will have demands.

Read Underwood’s full discussion on .