Mark Zuckerberg, the founder and chief executive of Facebook, officially opened the day's trading on the Nasdaq exchange this morning by remotely ringing the bell from outside his California headquarters.
However, early trading was delayed until 11.30am local time due to the sheer volume of shares being bought and sold. According to media reports, more than 82m shares were traded in just the first 30 seconds.
Shares in the eight-year-old social network, initially priced at $38, rose to $43 within the first few minutes of trading.
That would value the company at $115bn, making it bigger than General Motors and Boeing, but not quite as large as Coca Cola, Amazon or HSBC.
The share price has now dropped back to around $39, one dollar above the IPO price, although it is expected to climb over the day's trading.
Facebook's initial public offering (IPO) is the third-largest in US corporate history, behind financial giant Visa and car maker General Motors.
Owners of the social network are releasing just under a fifth of the company's total shares, about 421m, which could raise up to $18bn for the company.
The IPO is the most hotly anticipated technology stock flotation since Google in 2004. US search giant Google's stock started trading at $85 but ended the day at $100.34. Its shares now sell for more than $600.
Facebook's stock flotation instantly sent Zuckerberg into the top tier of the super wealthy, with estimates that his stake in Facebook is worth $19.1bn.
Fellow founders Dustin Moskovitz and Eduardo Saverin also become paper-billionaires overnight, with around $5bn each, while Napster founder and former Facebook employee Sean Parker, and Facebook's current chief operating officer Sheryl Sandberg also join the billionaires club.
Other parties set to benefit from the share sale include Microsoft, US frontman Bono and Silicon Valley investor Peter Thiel, as well as US venture capital firm Accel Partners and Russian digital investment firm Digital Sky Technologies.
Alongside the big winners, it is thought that the IPO will make hundreds of millionaires overnight, including artist David Choe, who famously accepted payment in stock rather than cash for painting a mural on Facebook's California base. His stock is expected to be worth more than $200m after the float.
But new shareholders will not have much say over how Facebook is run, as only A shares are being made available, which carry just one share per vote, compared to the 10 shares per vote carried by the B shares held by the current owners.
Facebook's owners will control more than 96% of the votes even after the public listing, with founder Zuckerberg holding 56% of the voting power and still owning 25% of the company.
Employees at Facebook's Menlo Park campus in California have been up all night ahead of the float, taking part in one of the company's trademark "hackathon" events aimed at coming up with new ideas for future services.