Although the definition varies, millennials (also known as Generation Y) are typically considered to be those people who reached legal age around the turn of the 21st century. Currently, millennials comprise approximately 33 percent of the global work force, and estimates from the BPW Foundation project that by 2025, that number will increase to 75 percent. In short, millennials are the future of your business, and they must be managed effectively — and included in your succession planning.