Alphabet

Market cap
$1.95 trillion

Stock return since pre-pandemic high*
92%

Strengths
Alphabet’s Google unit commands about 30% of the digital advertising market, according to eMarketer. That business is a profit-generating machine, with YouTube adding high-octane fuel to its engine. 

Threats
Regulators in the U.S. and Europe are pursuing a range of antitrust cases against Alphabet, arguing that the connections between Google’s search and ad businesses are anticompetitive. Alphabet says that its methods are fair and transparent. Still, any court defeat or settlement that changes its business model could ding profits and startle shareholders. 

Amazon

Market cap
$1.81 trillion 

Stock return since pre-pandemic high 
65% 

Strengths
The pandemic has only deepened our addiction to e-commerce, where Amazon dominates, and its pioneering cloud-service business remains by far the market leader. Both businesses are inflation-proof.

Threats
Retailers big (Walmart, Target) and small (the many customers of Shopify) are getting better at e-commerce, and more competition could mean more modest growth. Amazon’s shares trade at 70 times earnings (far above the S&P 500 average of 24), and investors may lose some enthusiasm if Amazon’s trajectory flattens out.

Apple

Market cap
$2.64 trillion

Stock return since pre-pandemic high 
102% 

Strengths
Apple’s ecosystem of higher-end tech products—encompassing iPads, iPhones, and computers, apps, and services like Apple Music—keeps consumers loyal. It also generates great margins: Apple has been the most profitable company in the Fortune 500 for six of the past seven years. 

Threats 
The global semiconductor shortage is a huge headache for a company that ships as much hardware as Apple. The company said the chip crunch cost it more than $6 billion in lost revenue in the most recent quarter. A court ruling in September, meanwhile, requires Apple to let iPhone developers point consumers to payment options outside its App Store, a move that could harm the store’s profits.

Microsoft

Market cap
$2.55 trillion

Stock return since pre-pandemic high 
84% 

Strengths
A company once known almost exclusively for Windows and Office has evolved to encompass cloud services (Azure), a thriving gaming platform (Xbox), cybersecurity and A.I. Like Apple, its offerings tend to be “sticky,” with customers coming back regularly to deliver predictable revenue growth.

Threats
Microsoft’s cloud business, its biggest recent success story, faces hefty competition from fellow trillionaires Amazon and Google, among others. And web-based productivity tools continue to shrink Windows’ market share.

*Stock returns from 2/19/20 through 11/22/21; market cap as of 11/22/21.

A version of this article appears in the December 2021/January 2022 issue of Fortune with the headline, “Can the trillionaires be toppled?”