Expedia Inc. just vastly broadened its lodging options by partnering with the world’s largest vacation rental provider, HomeAway, to offer its vacation rentals on Expedia.com in the U.S. and Mexico.

HomeAway’s stock spiked last week over rumors about merger and acquisition activity. There were no mergers, but perhaps HomeAway’s Expedia partnership triggered the activity.

In addition to hotels, Priceline’s Booking.com displays apartment hotels, villas and some vacation rentals, but the pilot Expedia-HomeAway partnership takes a larger step, and may not be particularly appreciated by Expedia’s huge roster of chain hotels.

“This is a significant milestone for the vacation rental industry and for realizing HomeAway’s mission to make every vacation rental in the world available to every traveler in the world,” says HomeAway CEO Brian Sharples of the Expedia partnership. “As one of the most visited online travel agencies, each month Expedia.com will give millions of travelers the opportunity to discover the benefits of booking a vacation rental, and we look forward to also helping our customers increase the visibility of their properties.”

This is a somewhat risky move for Expedia as it doesn’t want to detract from its all-important hotel business, and this is likely why it has taken Expedia so long to partner with HomeAway on vacation rentals.

Still, the lodging world is changing because of the proliferation of vacation rentals and the sharing economy reflected in the rise of companies such as Airbnb.

Expedia’s HomeAway partnership, which is slated to go live early in 2014, reflects this new reality.

Asked in what form the Expedia-HomeAway partnership will be implemented and whether the vacation rental offerings will be displayed on Expedia.com or Homeaway, Victor Wang, a HomeAway spokesperson, said “the exact booking process flow has not yet been finalized.”

And, what happens after the pilot programs wraps up?

“After the pilot program, we will evaluate how to best make more vacation rental properties available through Expedia,” Wang said.

Wang declined to comment on the business model and whether HomeAway will pay Expedia a commission.

As of the end of 2012, HomeAway operated 44 websites in 13 languages, offering vacation rentals, condos, villas and cabins in 171 countries.

Expedia already had a small-scale partnership with HomeAway’s BedandBreakfasst.com.

Coming on top of its partnership to power Travelocity sites in North America to boost hotel bookings, slated for next year, Expedia will have on its plate in 2014 with this new HomeAway partnership, as well.

Photo Credit: A vacation rental in Austin that has been rented through HomeAway. Heather Cowper / flickr