Pinterest has raised $100 million in funding in a round led by Rakuten Inc. with participation from existing investors Andreessen Horowitz, Bessemer Venture Partners, FirstMark Capital and a number of angels.

The two companies said the investment is part of a strategic partnership between Rakuten and Pinterest to help expand in Japan and into Rakuten’s 17 other global markets.

One of the largest Internet companies in the world, Rakuten’s flagship operation is Rakuten Ichiba, the largest e-commerce site in Japan and one that the company describes as having a “business-to-business-to-consumer model.”

Rakuten’s involvement could indicate how Pinterest intends to generate revenue, a puzzle it has not yet cracked. A retail component would fit easily into what’s already happening with Pinterest. There are a large number of retailers who use the platform as a shareable and flexible complement to their own websites and catalogs, for example. Additionally, a major way that consumers use Pinterest is to collect and organize photos of items they’re considering purchasing but that need coordination, such as the elements to redecorate a room, personalize a fashion trend, or design a wedding.

Rakuten has expanded globally by making acquisitions that so far have included (U.S.A.), Priceminister (France), Ikeda (now Rakuten Brasil), Tradoria (now Rakuten Deutschland) and (U.K.), along with investments in and AHA Life.

“While some may see e-commerce as a straightforward vending machine-like experience, we believe it is a living process where both retailers and consumers can communicate, discover, and curate to make the experience more entertaining,” said Hiroshi Mikitani, CEO of Rakuten. “We see tremendous synergies between Pinterest’s vision and Rakuten’s model for e-commerce. Rakuten looks forward to introducing Pinterest to the Japanese market as well as other markets around the world.”

According to comScore, Pinterest has more than 20 million users, up dramatically from the 1 million it had in July 2011. Founded in 1997, Rakuten is headquartered in Tokyo, with over 10,000 employees and partner staff worldwide.

Ben Silbermann, co-founder and CEO of Pinterest, said: “Our goal is to help people discover things they love, by connecting people through their shared interests. Bringing Rakuten on board gives us an amazing opportunity to move a step closer to this goal.”

Related links:

Rakuten – press release

Rakuten – corporate site

All Things D – Exclusive: Japan’s Rakuten Wins the Heart of Pinterest in $100M Funding Race With $1.5B Valuation

Wall Street Journal – Pinterest Raises $100 Million With $1.5 Billion Valuation

The Next Web – Pinterest set to announce new funding at $1 billion valuation, with an eye on ecommerce