In the past two years, Amazon\u2019s (NASDAQ: AMZN) advertising sales have taken off to such an extent that many are now wondering whether Google\u2019s (NASDAQ: GOOGL) business is in fact under threat. Amazon doesn\u2019t specifically report its ad revenue. It reports an \u2018other\u2019 segment which is generally considered to consist mainly of advertising revenue. In the first quarter of 2019, the segment generated $2.72 billion, a 36% increase from a year earlier, although this did mark a slowdown from the growth recorded in previous quarters. Last year the segment\u2019s quarterly year-on-year growth was between 95 and 138%. In 2017, the segment\u2019s revenues were 57% higher than they were in 2016. While ad sales have slowed slightly, for now, there is no question that Amazon\u2019s advertising business has momentum. In fact, by some measures, the segment is growing faster than Amazon\u2019s cloud business, AWS, was growing at the same stage of its own life cycle. And like AWS, the advertising business represents a supplementary revenue stream which few had anticipated. Google\u2019s Ad Revenue Sees Major Slowdown Google, and parent Alphabet,\u00a0 meanwhile saw its ad revenue growth slow to 15% in the first quarter of this year, its slowest growth rate since 2016. Anecdotal evidence does suggest that Amazon is taking market share away from Google, as well as from Facebook (NASDAQ: FB). A survey of retailers who use online advertising by performance marketing agency Nanigans found respondents are already spending 14% of their digital advertising budgets with Amazon. That\u2019s still less than the 21% that goes to Google and the 19% going to Facebook, but Amazon has clearly caught up very quickly. Amazon is also earning the lion\u2019s share of ad budget increases. These figures represent a narrow segment and don\u2019t yet represent the digital advertising industry as a whole, but they do point to where the industry is heading. Primed to Buy Buyers of digital advertising space believe customers searching for a product on Amazon are closer to being ready to buy, than they may be when searching on Google. Many customers already have their credit card details saved on Amazon\u2019s database and making a purchase can literally take just one click. This may give advertisers a better and more measurable ROI. For Prime customers, the incentive is even higher, as delivery is free or discounted. Many products are already heavily discounted on Amazon, and customers are well aware that the deal available on Amazon is about the best they will find. Google Still Offers a Unique Proposition Although Amazon\u2019s advertising business is quite new and still evolving, the story is compelling. 2019 is set to be the year that digital advertising overtakes traditional advertising in the global economy, and Amazon is in a strong position to make sure it earns a large chunk of that spending. Some of that may come at the expense of Google, and to a lesser extent Facebook, but that doesn\u2019t mean their business models are in trouble. Google represents a larger audience and a larger range of industries than Amazon does. While Amazon may dominate e-commerce for several categories, there are others where it does not. These include financial services, automotive industries, travel, and real estate to name just a few. Advertisers will also be reluctant to be too dependent on Amazon. Ultimately, they will want to spread their budget. For now, that means gains for Amazon \u2013 but it\u2019s unlikely it will overtake Google by a large margin. Facebook is less at risk. First, Amazon and Google are both competing head-on for search-based advertising. Facebook\u2019s model is quite different and is based on demographics, interests, and online habits. Facebook also offers an audience to a wider range of advertisers. Amazon may still have plenty of upside in the advertising business, but it doesn\u2019t signal an existential threat to Google or Facebook. If anything, the existential threat will be to traditional media companies that really are in danger of becoming irrelevant.