In today's world of high-speed trading and short attention spans, it might seem unfathomable to hold any given stock for years, let alone decades. But the world's best investors know all too well the best way to consistently beat the market is to buy high-quality stocks and hold them for extended periods.

To that end, we asked three Motley Fool contributors to each discuss a growth stock they think investors could do well to buy and hold for the next 50 years. Read on to learn why they chose Alphabet (NASDAQ:GOOG)(NASDAQ:GOOGL), iQiyi (NASDAQ:IQ), and Shopify (NYSE:SHOP)

Old fashioned pocket watch on top of 100-dollar bills.

IMAGE SOURCE: GETTY IMAGES.

OK, Google, where will you be in 50 years?

Steve Symington (Alphabet): It's easy to forget that Google was only founded just over 20 years ago. Since then, the internet titan has already amassed eight products which each boast at least one billion (yes, with a "b") monthly active users, including Google Drive, Chrome, Android, Search, Maps, YouTube, Gmail, and the Google Play Store.

But even putting aside its massively profitable, fast-growing core business (Google revenue climbed around 17% year over year last quarter, to over $36 billion), one big reason Google restructured three years ago to operate under its new parent company, Alphabet, was to provide investors more insight into how it's putting money to work in other early-stage, high-potential projects.

These projects are collectively held under Google's aptly named "other bets" segment, and include companies like Waymo, for self-driving vehicles; Calico, with its focus on extending human lifespans; Loon, for LTE connectivity delivered with high-altitude balloons; Wing, for drone delivery; Fiber, for high-speed internet; and Verily, with its life-sciences products.

If any one of these companies manages to realize its full potential, we should be looking at a significantly larger Alphabet decades from now.

Capitalize on the growth of streaming and foreign markets 

Keith Noonan (iQiyi): China's tech sector is known for volatile pricing swings, and with the country's economic growth slowing recently and no clear end in sight for the trade disputes with the U.S., the risks that come with investing in developing markets are at the forefront of investors' minds. That said, investing in high-quality companies from China and other fast-growing markets is a way to prepare your portfolio for a potential future in which these governments and economies are significantly more powerful on the world stage. For investors seeking exposure to China's tech and entertainment markets, iQiyi stock is a standout candidate at current prices.

iQiyi was spun off from Baidu last year, a pedigree that's given the media offshoot strengths in targeting advertising, potentially revolutionary categories like artificial intelligence, and a wide range of future opportunities as the two companies continue to maintain a close relationship. Often described as a Chinese Netflix, iQiyi also has an advertising-based service but has pivoted to make premium subscription videos the core of its business. The company has increased its paid subscriber rolls from just 5 million in May 2015 to 87 million at the end of last year, and it's on track to hit 120 million premium subscribers in 2019.

Only around 20% of Chinese families subscribe to iQiyi, while nearly 70% of American families subscribe to Netflix. If you consider that China has over a billion more people than the U.S. and assume cautiously optimistic positions for the long-term growth of the country's middle class and per-capita discretionary spending, iQiyi's massive growth potential should start to become apparent. Add in the fact that it's ramping up its video game business, making significant pushes in categories like virtual reality and short-video social media platforms, and having success with its analytics-based content development initiatives, and it's easy to see that iQiyi is making smart moves to turn potential into reality. 

Tap into this growing e-commerce play

Chris Neiger (Shopify): If you're looking for a fast-growing company that probably has decades to benefit from the expanding e-commerce market, then Shopify is your stock. The company's platform and services help business of all sizes sell their products online, and over the past few years Shopify has been on quite a roll.

Shopify provides its customers with everything from order tracking and online marketing to credit card processing. Its jack-of-all-trades e-commerce services is paying off, and the company has built out a customer base of 800,000 businesses. In the most recent quarter, Shopify's sales jumped 50% year over year. Its impressive sales growth -- and the fact that it's benefiting from what will be a $24 trillion e-commerce market by 2025 -- has made investors bullish on Shopify and pushed its share price up 95% over the past year.

Shopify isn't profitable right now, and its share price isn't cheap, trading at about 24 times its sales, but the company is still at the very beginning stages of benefiting from e-commerce. With its growing list of customers and the fact that the company is already leading the charge into the fast-growing e-commerce market, it's likely that Shopify's stock will benefit for years to come.

The bottom line 

Of course, much can change over the years, so we can't guarantee these stocks will go on to deliver outsize returns. But there's no denying their potential is enormous, from Google's already dominant position and supplementary "other bets," to iQiyi's early leadership in China's media-streaming space, and Shopify's massive and growing total addressable market.