More than 5 billion people — two in every three living on the planet — are now connected on mobile devices, and it’s estimated that three-fourths of the global population will have a connection by 2020.

As the ranks of mobile users continue to swell, the mobile device is assuming more importance than ever in e-commerce, where mobile accounts for a growing share of consumer spending. One in four e-commerce dollars is now spent on a mobile device, and 62 percent of smartphone users say that they’ve made a purchase using their phones within the past six months.

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Given these trends, it’s no surprise that brands large and small are devising their mobile e-commerce strategies, with an eye toward claiming their slice of an expanding pie. Here are five reasons companies can’t afford to ignore the surging mobile e-commerce market:

1. It’s a rapidly growing industry

Mobile e-commerce sales reached $1.36 trillion in 2017, a 40 percent increase over 2016 sales. The coming years will see a steady rate of growth, with forecasters projecting $3.56 trillion in total sales by 2021.

By that point, according to eMarketer, mobile could account for nearly three-quarters of the total e-commerce sales. A key driver of this growth: The dramatic improvement of mobile advertising in light of the significant enhancements to consumer targeting from cross-device and offline conversion data. Google has been at the forefront of these improvements, with its analytics tools affording advertisers unprecedented insight into consumer behavior. Leveraging this data to direct consumers to take desired actions, advertisers are sending mobile e-commerce to new heights.

2. Mobile e-commerce users show higher value than desktop users

Think about why a consumer might make a purchase on her smartphone. She’s on the go, she knows what she wants, and she prizes efficiency.

This move of consumers to mobile corresponds directly with improved technology, which has changed targeting and efficiency for the better. Retailers now know that this consumer bought a dress in H&M and based on that can offer a slew of incentives and benefits that encourage her to continue shopping.

We have seen that this kind of communication with the consumer does urge them to make purchasing decisions, making the case for mobile advertising clear.

Statistics show that compared to e-commerce users on desktop, mobile shoppers spend up to four times longer on mobile apps, are less likely to abandon their carts, place more expensive orders, and are more likely to return for another purchase.

Simply put, meeting high-value users where they are means meeting them on mobile.

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3. Mobile is uniquely suited to AR and VR

As virtual reality (VR) and augmented reality (AR) solutions are increasingly integrated into the shopping experience — enabling consumers to, say, envision a kitchen renovation, or try on the same blouse in different colors — advertisers will be able to interact with consumers in truly innovative, interactive ways. Mobile is already playing a central role in the introduction of these tools.

Snapchat’s “Shoppable AR,” adopted by brands including Clairol, Adidas, King, and STX Entertainment, has been hailed as a harbinger of future trends in advertising, and Facebook recently announced that it will allow advertisers to showcase their products with AR ads in users’ news feeds.

4. Voice assistants will drive continued growth

The increasing popularity of voice assistants presents a plethora of opportunities for advertisers, and much of the action will concentrate on smartphone tools such as Apple’s Siri.

A Capgemini analysis finds that within three years, 40 percent of e-commerce consumers will use voice assistants instead of visiting web pages or using apps, while 31 percent will use a voice assistant rather than visit a brick-and-mortar location.

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5. Mobile wallets will make mobile e-commerce even more attractive

Consumers already see convenience as one of mobile e-commerce’s biggest selling points, and the growing integration of features such as mobile wallets will bring even more convenience and efficiency to the e-commerce experience.

Mobile wallets, which enable users to send or receive money on their mobile devices, constituted a $594 billion global market in 2016. By 2022, the market will reach $3.147 trillion in value, according to Zion Market Research.

Moreover, with the online retailer, Overstock, introducing the option for customers to pay in bitcoin — sparking $300,000 in monthly bitcoin purchases — other retailers may move in the coming years to introduce cryptocurrency payment options, attracting new consumers and propelling revenue growth.

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As more consumers vote not with their feet, but with the taps of their fingers, it will be essential for advertisers to optimize their campaigns for robust mobile e-commerce growth. Those who can satisfy consumers’ craving for highly relevant, seamless experiences will thrive in the coming era of mobile dominance in e-commerce.