Alphabet (NASDAQ: GOOG)(NASDAQ: GOOGL) subsidiary Google, along with Facebook, are the market leaders in the digital ad space. Its 10-year return from January 2010 to December 2019 was an astounding 405%, and Alphabet was one of the hottest tech stocks of the decade. As Alphabet begins a new decade, it's in a strong position to continue providing excellent results to its shareholders. Its primary source of revenue is online advertising, which also includes advertising on YouTube, and that grew over 20% in each of the last two full fiscal years. However, that growth has been slowing recently, with trailing-12-month (TTM) advertising revenue up just 17% compared to a year ago. Given that Google is the market leader in search, it's in an excellent position to capitalize on the shift in ad dollars moving from TV to online. As the proliferation of low-cost mobile devices reaches the broader population in developing economies, the opportunities for Google to monetize search requests will expand.