The US-headquartered giant now boasts around 25 million sellers and 157 million buyers and has a stock market value of more than 32 billion US dollars (£21 billion).
Computer programmer Pierre Omidyar began the business as a sole trader in 1995, listing a broken laser pointer pen as his first item for sale - and being stunned to find a buyer.
And from one entrepreneur's success story, eBay has since sparked an army of start-ups, giving small firms the power to sell around the world.
There are now more than 2,000 eBay millionaires in Britain alone as savvy sellers - from so-called mumpreneurs to graduates - tap into the site's unique market where there's a buyer for almost anything.
Academic and business forecaster Professor Richard Scase said: "Governments try to create entrepreneurs and generally fail.
"Over the past 20 years eBay has done it for more than 25 million sellers."
He added that eBay has transformed business and retailing, "destroying the relevance of geographical and national boundaries".
"With tablets, laptops and smartphones, teenagers through to pensioners can be international traders," he said.
In Britain, there are over 200,000 businesses trading through eBay, up from around 123,000 six years ago.
The site first arrived on these shores in 1999 and now attracts 18 million visitors every month.
One of eBay's recent British business successes includes children's gifts and accessories firm Thingimijigs, set up by mumpreneur Rachael White 10 years ago from her kitchen table with just an eBay account and £200.
The 43-year-old left her career at supermarket Morrisons to launch on her own and now makes more than £1 million in annual revenues, selling products worldwide from a purpose built facility in Lancashire.
More than half the small online retailers on eBay's UK marketplace are now global - exporting to four or more different continents.
The site has played a key part in enabling firms to become exporters without the costs and infrastructure usually needed to trade internationally.
Sarah Calcott, director of operations at eBay UK, said: "We're working hard to ignite the entrepreneurial spirit of small businesses, providing them with the tools and the flexibility to export millions of British goods abroad, despite lacking the infrastructure of a traditional exporter."
In May, eBay's global shipping programme - which is used by up to 10,000 UK sellers a day - took its millionth order.
The group has also worked hard to bring eBay onto smartphones and tablets in recent years.
Its app has been downloaded 280 million times across the world, but has really taken off in the UK, as has its click and collect service following a tie-up with Argos two years ago.
Buyers can now pick up from 750 Argos stores, with 2.5 million parcels going through the network and eBay is looking to expand the tie-up further.
Ms Calcott said one of the biggest challenges for eBay is keeping pace with the demands of consumers and sellers, especially around key selling times, such as Black Friday and Christmas.
"Whether it's buyers wanting their products super quick or sellers wanting the tools to make it easy to do business with eBay, that's the biggest challenge," she said.
She said the group has plenty of innovations planned ahead, such as building on its mobile capability further and growing international services for sellers.
And for the next 20 years, eBay aims to help the next generation of entrepreneurs get off the ground and thrive.
"Selling can be very easy to do on eBay and for many businesses, it's changed their lives," said Ms Calcott.
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