More than one-third of the United States work force is between the ages of 18 and 34, indicating that Millennials have surpassed Generation X to represent the largest share of the American work force. Unfortunately, today's business leaders are not well-equipped to deal with the mindset and motivations of this new generation.

But some companies have figured Millennials out, and know how to maximize their unique talents and needs. Infusionsoft, a small-business email service provider located in Chandler, Arizona, is one of Forbes' "100 Best Workplaces for Millennials." Game rooms and snacks are only part of the equation. Employees at Infusionsoft report enjoying a fun and cooperative work environment, feeling genuinely appreciated for their contributions, and being able to take time off when needed.

Unfortunately, too many companies simply assume what Millennials want and barely scratch the surface when trying to recruit and keep them. Companies offer perks Millennials simply don't value, while skimping on what does matter to them. This can create mass turnover. To help you stem the flow of quality employees from your organization, here are five reasons your Millennial employees are quitting--and what to do about it.

1. You Don't Provide Meaningful Work

Surveys show that 30 percent of Millennials consider meaningful work to be the most important factor in making them feel successful in their jobs. By contrast, only 11 percent of hiring managers thought Millennials needed it. This disconnect leads Millennials to quit companies in droves.

To provide meaningful work, help young professionals understand the contribution their job makes to the mission of the company. Let them see the big picture, and show them firsthand how a successful company functions. Let them see their role as part of a larger whole, and help them embrace the meaning this creates in their work. Help them see where their career can take them and the potential impact made as they advance in the company.

Here's what to say: "I've assigned you this task because it's needed to get this major project off the ground. If successful, this project has the potential to impact 1,000 of our customers."

2. There's No Sense of Accomplishment

Too many companies have turned specialization into an art form, with employees doing the same repetitive work day after day. There's no sense of connection, and no sense of accomplishment. Meanwhile, 24 percent of Millennials say a sense of accomplishment is the most important factor in feeling successful at work. If this doesn't exist in your company, you can expect your team to lose interest and move on.

To build a sense of accomplishment, offer plenty of detailed feedback. Help Millennials know which areas they're thriving in and where they can improve. Don't save your compliments and coaching for quarterly or yearly reviews. Instead, find a way to connect with Millennials and give weekly feedback. This type of engagement helps young professionals feel secure in the direction their work is going, and assures them they won't be ambushed by a negative review.

Here's what to say: "I saw that you put some extra effort into your presentation last week. Thanks for going the extra mile to make it special."

3. Employee Feedback Isn't Respected

Millennials aren't interested in old-school corporate hierarchies, and the days when top-down management made companies successful are fading fast. If employee feedback is downgraded or simply not welcome at your company, expect your Millennial employees to look elsewhere for work.

Instead, encourage two-way communication. Millennials enjoy being team players and want to make a positive contribution to the company. Giving feedback to young professionals while also inviting them to give you their thoughts encourages their sense of value. However, expect honest feedback--Millennials aren't known for their adherence to unspoken corporate rules.

Here's what to say: "I want to get your opinion on this upcoming project. What do you think is the best way to move forward?"

4. There's No Flextime

Millennials no longer believe job security is offered at any company, and are much more likely to "shop around" and compare job benefits. A lack of flexibility in their work or hours is a big reason Millennials quit. If your company doesn't offer flexible work arrangements or the possibility to work remotely, you're lagging behind the trend and unlikely to retain young professionals.

Instead, allow those who meet specific standards to take advantage of flexible options. Arrange for qualified employees to take time off, or to make up hours to attend to important personal matters, or to work remotely one or more days per week. Take inspiration from Netflix and focus on productivity rather than hours while still running a wildly successful company.

Here's what to say: "What's most important to me is that the work gets done. If you'd be more productive working from home a few hours a week, just let me know."

5. Poor Communication Is the Norm

No one wants to work at a company where the communication is poor, and Millennials will be the first ones out the door if your company operates this way. Having grown up in the information age, young professionals have come to expect hyper-connectivity and the ability to always know what's going on with everyone.

While all-inclusive communication just isn't practical at a company level, there are many things that can be done to encourage more transparency. Make sure that expectations are crystal clear--a report due at 5 p.m. is better than a report due "soon." Also, make sure nonverbal communication matches what is said--actions still speak louder than words.

Here's what to say: "We're expecting to grow 17 percent this year, but we do anticipate some challenges. Here's what they are, and here's how you can help."

Keeping Millennials happy isn't rocket science, but it does require a shift away from the old ways of doing business. By providing meaningful work and a sense of accomplishment, taking employee feedback seriously, offering flexible work options, and keeping communication flowing, you'll be well on your way to retaining Millennial employees.

What issues do you see in retaining Millennials at your company? Share in the comments!