Amazon's (AMZN  ) third annual Prime Day - a single-day shopping bonanza offering steep discounts on hundreds of thousands of products and services - begins on July 10 at 6 p.m. ET/9 p.m. PT. The event has grown in scope and size since it was first introduced in 2015 to honor Amazon's 20th birthday; 2016 Prime Day sales were 60% higher than in 2015.

To keep momentum going, Prime Day 2017 will be available in 13 countries, including Austria, Belgium, Canada, China, France, Germany, India, Italy, Japan, Mexico, Spain, the US, and the UK. Prime Day 2017 will also last longer than ever before: 30 hours, or through July 11, not to mention select deals available even before July 10.

Amazon has already increased its Prime subscription base, with estimates indicating that US membership has doubled in past two years. Since Prime members are Amazon's bread and butter; they spend an annual average nearly twice that of non-Prime customers, likely trying to maximize the benefits of their membership. Amazon uses Prime Day to lure new subscribers into the fold.

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To that end, Prime Day deals are only available to existing Amazon Prime members, though customers who don't want to commit to paying the annual Prime subscription fee can sneakily opt in for a 30-day Prime trial to take advantage of deals.

Prime Day is not only a tool to bump up revenue and increase Prime membership, but a way for Amazon to promote its own services and products.

Amazon has hinted that they will have particularly good deals on televisions this year both due to a record level of inventory and as a kind of promotional tie-in to Amazon Fire, its TV streaming service. Amazon will offer price reductions at Prime Pantry, continuing a trend of pushing grocery sales that perhaps began with its recent acquisition of Whole Foods. Amazon will also have deals on its own line of voice-activated products and Amazon Music Unlimited.

Deals will be introduced continuously throughout the day. "Lightning deals," or short-term, deeply slashed prices on coveted limited stock items like electronics, will keep pressure to purchase high.

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Amazon will not be the only outlet hosting "Black Friday in July" sales. More conventional brick-and-mortar stores, such as Macy's (M  ), Best Buy (BBY  ), and Nordstrom (JWN  ), amongst others, will also have promotional events, offering free shipping and product discounts both online and in stores in a bid to rival the e-commerce giant.

In past years, big-box stores like Walmart (WMT  ) and Target (TGT  ) have had their own Prime-Day type events. It is unclear if these will be repeated in 2017, though time is running out to generate buzz for these events through ad messaging.

Walmart has already made other efforts to directly challenge Amazon's online retail dominance with the 2016 acquisition of Jet.com and recent slashing of free-shipping thresholds.

While competitors can benefit from a Prime Day boost, it is possible that these corollary sales may have the undesired effect of increasing Prime Day's publicity and driving up consumer awareness of Amazon: a recent Market Watch survey suggested that a sharp increase in consumers who said they would participate in Prime Day 2017 from 2016 might be attributed to this.