According to the Global Business Travel Association (GBTA), business travel spending topped $1.2 trillion worldwide in 2015.

"Business travel has demonstrated a tremendous resiliency as it continues slow and steady progress even in the face of global uncertainty, a weakened global economy, terrorist attacks, world health issues and other obstacles," said Michael McCormick, executive director and chief operating officer of GBTA.

As business travel continues to grow worldwide, the face of business travel is also evolving — thanks to millennials.

Bleisure travel has arrived

More than just a trend or a buzzword nowadays, bleisure travel is gaining popularity. In a survey by BridgeStreet Global Hospitality, 60 percent of international travelers have taken bleisure trips — mixing business with leisure.

"Employees feel bleisure opportunities benefit them and add value to work assignments, contributing to higher job satisfaction and loyalty," said Kelly Murphy, BridgeStreet Global Hospitality vice president of marketing during a panel discussion at a recent Serviced Apartment Summit.

Millennials especially are embracing bleisure travel.

In a survey by Expedia, employees under 30 travel 4.7 times per year on business, compared to the 3.6 times of business travelers between the ages of 30-45. The survey also found 62 percent of millennials are more than likely to extend their business trip into a personal vacation.

What are millennials looking for in business travel?

By the year 2020, millennials will not only make up 50 percent of the global workforce, but they will also account for almost 50 percent of all business travel spending.

Poised to become the biggest business travel clientele, millennials are looking for certain things when it comes to business traveling.

According to the Traveler Satisfaction: Exploring the Generational Divide in Business report by GBTA and American Express Global Business Travel, airport security wait times were found as the top annoyance among all business travelers.

"This is one of the biggest hindrances to expedient travel today," reads the report. "It is interesting that almost half (45 percent) of frequent business travelers have TSA Precheck. This means it is something travelers consider highly valuable, yet most companies do not cover the cost for TSA Precheck or Global Entry. Taking all this into consideration, companies could offer to cover the cost of TSA Pre and/or Global Entry for their employees that travel on a frequent basis."

The biggest difference between the generations in this report was the control travelers wanted when planning a business trip.

Millennials were found to be more satisfied when they have the choice to book from different travel companies and book through third-party sites such as an online travel agencies (OTAs). Gen Xers want control over their trip, and baby boomers didn't care about the booking process as long as the travel experience went smoothly.

"Millennial business travelers want a variety of suppliers from which you can choose to book and prefer booking travel on a third-party website," according to the report.

How are brands adapting?

As business travel morphs in the 21st century, brands are learning to adapt with new business practices.

Airbnb is already changing the travel industry as the sharing economy continues to play a dominant role. The home sharing business has gone back to its roots, so to speak, as it refocuses some of its efforts on business travel. In recent years, Airbnb has been increasing its focus on business travel by integrating with travel management systems, such as the American Express Global Business Travel and BCD Travel.

According to Airbnb, business travel on its site has grown three times since July 2015.

"Business travelers want convenience, where they can get good Wi-Fi, an ironing board and hair dryer ... things you accept in traditional accommodations," Julian Persaud, Airbnb's Regional Director of APAC, told CNBC.

Some of the listings on Airbnb's website are specified as business travel ready, which means hosts don't have pets and don't allow smoking.

Airbnb says it sees 14,000 new companies each week sign up for its business travel services. They credit the shift to younger business employees who sign up to use their services.

"Particularly, millennial employees have higher expectations of how they spend their time and wanting to move away from traditional methods," Persaud said. "They're the ones knocking on the doors of their boss, saying, 'hey we want to do this.'"

Airbnb is not the only travel brand looking to gain business travelers.

Concur, one of the big players when it comes to travel and expense platforms, recently bought flight and search site Hipmunk for an undisclosed amount. Concur hopes the acquisition will help improve its platform for business travelers with the addition of stronger search capabilities through Hipmunk.

"Six years ago, our vision was to take the agony out of travel and travel planning," said Adam Goldstein, co-founder and CEO of Hipmunk, in a statement. "This combination means we can do an even better job for frequent travelers, in both their leisure and business travel."

Bring on the perks

Perks that travel brands offer also seem to change as millennials become the face of travel.

According to Spafinder Wellness 365, younger travelers are seeking perks such as clean cuisine, high-tech exercise facilities, complimentary fitness classes and spa services when planning a trip.

Earlier this year, hotel brand Westin embraced the growing trend of wellness travelers by creating a new branding identity that catered towards well-being. The campaign uses strong visuals of individuals working out or eating healthy while using the taglines: "Sleep Well, Feel Well, Eat Well, Move Well, Work Well and Play Well."

"As a brand, we're trying to provide people an experience that lets them tap into their well-being while traveling," said Westin’s Global Brand Leader Brian Povinelli. "The new identity is very lifestyle driven. I think other brands in the hotel space are still in the old paradigm of showing meeting spaces and pools and beaches and guest rooms, whereas we're showing the lifestyle we want the brand to portray through visual identity."

Advito predicts the global business travel market will continue to grow in 2017.

"Emerging markets are set for a stronger economic performance in 2017," the report states. "At 4.2 percent, growth will surpass the 3.5 percent forecast for 2016. This improvement is largely driven by Latin America, primarily due to Brazil, which is expected to emerge from a prolonged recession, but also because of stronger growth from Argentina and Colombia."

Millennials will certainly have a hand in predicting the next new trends in business travel.