There's a lot at stake for both sides. Amazon has built a following, but wants to grow its business globally. Meanwhile, brick-and-mortar retailers struggle to keep shoppers from using their stores as showrooms to test out and try on items before buying them for less on Amazon.
The holiday season ups the ante. Both online and brick-and-mortar retailers can make up to 40 percent of their annual revenue in November and December. And this year, they're competing for the growing number of shoppers who are as comfortable buying online as in stores.
Holiday sales are expected to rise 3.9 percent to $602.1 billion, according to The National Retail Federation. Of that, about $78.7 billion is expected to be online, up 15 percent from last year, according to Forrester Research.
Here's how the fight is playing out:
One of Amazon's biggest advantages is its low prices. It can charge less for everything from TVs to T-shirts because it doesn't have the high costs of running physical locations.
Last year, some retailers offered to match the lower prices that customers find on websites like Amazon during the holiday season. And this year, more have made this a policy. Best Buy even is offering to refund the difference if a customer finds a lower price after they purchase something up until Christmas Eve. The strategy could eat into profits, but retailers hope sales will increase.
Staples is among retailers also offering the same discounts online and in stores during big shopping days like the day after Thanksgiving known also Black Friday. "We want customers to be able to shop however they want and whenever they want," said Alison Corcoran, Staples senior vice president.
Stores had long seen their physical locations as an albatross, but now they're using them to their advantage.
"Everybody was telling me ... 'These stores, that's really a liability that you have,'" said Hubert Joly, Best Buy's CEO. "Absolutely not. It's an asset that you have 1,000 warehouses strategically located close to the customers."
Best Buy is among the retailers using their locations as distribution hubs from which they can ship goods that are ordered directly to customers' homes. Wal-Mart, for example, said items ordered online and shipped from stores usually are delivered in two days or less — quicker than having them shipped from warehouses across the country.
But Amazon.com Inc. is widening its distribution network to offer speedier delivery, too. Amazon added 8 million square feet of distribution centers and hired 70,000 people to work in them. It also added 1,382 robots to its line to help get packages out the door. And it partnered with the U.S. Postal Service to deliver some packages on Sunday.
"This year we're able to be faster and have more in-stock items," said Amazon spokeswoman Julie Law.
Other retailers are trying to get shoppers into stores. Gap Inc. has expanded its service that allows shoppers to reserve items online, and then pay and pick them up within 24 hours at many of its Banana Republic and Gap stores.
And options that allow customers to order and pay online and then pick items up at stores are popular. That led Renada Skannal, 27, to go to Walmart.com to order protective gear that her nephew could wear when riding a bike her mother is buying him as a Christmas gift. Her mother picked it up at a store to save time and shipping costs. "I want to make things easier for me," said Skannal, who lives in Jackson, Miss.