At the time, the bet seemed risky, even foolhardy. The e-commerce giant had established its reputation as the “everything store,” but its profit margins, year after year, were puny or nonexistent. (The company was also spending a lot of money on a quirky side business involving warehouses full of servers.) What’s more, as an Internet retailer, it belonged to an industry that many investors were wary of, fearing a repeat of the dotcom bust and burnout.

Fast-forward to the end of 2017, and Allen, portfolio manager of T. Rowe Price’s Science & Technology Fund, has nothing but respect for the reluctant retailer. Amazon stock has returned almost 400% over the past five years. It’s now not only Allen’s top holding, but the biggest position of T. Rowe Price as a whole, a company with almost $950 billion under management. That quirky side business? It’s now Amazon’s market-leading cloud-services division, and the company has reported profits for 10 quarters in a row. The bottom line: Owning Amazon stock has been much more lucrative than stocking shelves.

Amazon’s stratospheric rise, of course, is one of the great success stories in technology. But it also represents something broader and more important for investors. The company has expanded to encompass a diversified range of businesses that make it, in a sense, a microcosm of the market in a single stock. And it embodies the powerful wave of change that has swept the economy since the financial crisis—one that has broken down the barriers between “tech stocks” and the rest of the market.

For starters, it may come as a surprise to many investors that, technically speaking, Amazon is not a tech stock. In the S&P 500 and other indexes, it belongs to the consumer discretionary sector, for companies that make and sell nonnecessities, alongside Nike, Walt Disney, and Starbucks. On the other hand, ask anyone whose toilet paper automatically arrives via Amazon subscription, and the e-commerce company seems more like a consumer staple. Amazon’s house-brand batteries now outsell Duracell online, and the company will now get upwards of $16 billion a year in annual revenue from a grocery store—Whole Foods, which it acquired over the summer. Add to that its $16 billion-a year cloud business, its Netflix-challenging video streaming, and rumblings that it may enter the pharmacy market, and there’s a sense that there’s no industry Amazon won’t conquer.

The evolving reach of Amazon has coincided with a reconstitution of the U.S. stock market. Tech companies now dominate the market to an unprecedented extent, comprising the five most valuable companies: Apple, Google parent Alphabet, Microsoft, Amazon, and Facebook. Without the tech sector, the S&P 500 would have returned 14.6% this year through late November; instead it returned 19.5%. And while its relentless expansion has made many investors nervous, money managers argue that it’s time to accept the tech giants as the blue chips of today. In other words, if you want to have any shot of beating, or even keeping up with the market, you can’t afford to avoid them.

But Katie Koch, global head of client portfolio management and business strategy for fundamental equity at Goldman Sachs Asset Management, also highlights a paradigm shift in the way investors should think about picking stocks and about diversification itself. Own tech’s Big Five, she says, “but be cognizant of the disruption that they’re trafficking in, and how that can create other winners and losers.” That disruption is omnipresent because there are now tech companies everywhere in the economy—companies whose central missions are technology-centric, and those in other sectors that are making technical innovations central to their business models.

The upshot of all this is that it’s now possible—and maybe sensible—to build an all-tech portfolio that can tap the incredible growth that technological innovation offers, while still being diversified enough to protect investors from risk. It’s akin to that period a few years ago when dietitians inverted the food pyramid, rethinking the “base”—the foods we were supposed to eat most often—and swapping out carbs in favor of more bountiful helpings of fruit and veggies. These days, for a healthy rate of growth, tech should form the foundation of the typical investor’s portfolio, going where banks and perhaps Big Oil used to be.

At the same time, money management pros are lightening up on industries where profits have been undercut by new technologies. Doug Ramsey, who oversees $1.5 billion as chief investment officer of the Leuthold Group, holds no energy, consumer staples, utilities, or telecom stocks. But he does have about a third of his portfolio in tech, and is considering raising his allocation. If that sounds like bubble ­behavior, consider that technology is still among the cheaper sectors, relative to historical valuations. It trades at 19 times expected earnings for the next 12 months, only a 4% premium to the S&P 500. That’s compared with the height of the dotcom boom, when tech valuations were 121% above the S&P 500 average. “There’s nothing like that today,” says Ramsey.

Tech is also one of the sectors where analysts expect to see the greatest earnings growth in 2018. Larry Puglia, whose T. Rowe Price Blue Chip Growth Fund has trounced the S&P 500 with annualized returns of 18.5% over the past five years (and 37% in 2017 alone), says that some of the same companies he avoided around the turn of the millennium are now among the biggest holdings in his portfolio, including Amazon (AMZN), Alphabet (GOOGL), and Microsoft (MSFT). (Facebook (FB), which came a generation later, is his No. 2 position.) One draw for Puglia: The switch to subscription pricing that has accompanied their growth. “Many of the technology business models have become more necessary and durable over time,” adds Puglia.

Can Main Street investors responsibly bet the bulk of their savings on such high-growth technology companies? Investors are finding that a more fluid definition of that category helps when crafting a market-beating portfolio. “Tech isn’t even its own stand-alone sector, because it has tentacles into all the other industries,” says Koch, ticking off its impact in retail (e-commerce), automotive (self-driving cars), banking (mobile payments), health care (big-data genomics), and more. Put another way: What isn’t a tech stock these days? “There are going to be very, very big supertrends happening,” Koch says, “but you need to be invested well outside the tech sector to get exposure to all of this, and maybe also outside the U.S.”

With that in mind, we talked with top money managers who helped us build a portfolio that’s 100% invested in technology—defined broadly—while still broadly diversified.

Here are our picks for 2018:

• 4 Best Tech Stocks to Buy for 2018—Instead of Buying Bitcoin
• The 6 Best Stocks to Buy for 2018 Before Robots Take Your Job
• The 5 Best Fintech Stocks to Buy for 2018
• Why McDonald’s Is One of the 3 Best E-commerce Stocks to Buy for 2018
• The 5 Best Emerging Markets Stocks for 2018: How to Buy the Amazon and Google of China
• The 4 Best Biotech and Health Care Stocks to Buy for 2018

A version of this article appears in the Dec. 15, 2017 issue of Fortune with the headline “Investor’s Guide 2018 Stocks and Funds: The All-Tech Portfolio.”