"An open-sourced mobile platform that's constantly being improved upon by the community and is available for everyone to use speeds innovation, is an engine of economic opportunity and provides a better mobile experience for users," said Andy Rubin, senior director of mobile platforms for Google.
Developers can find Google's Android source code on the website for the Android Open Source Project.
The first Google Android phone - T-Mobile's G1 - went on sale in the US today but won't hit the UK until next week.
Google expects that by making the source code for the operating system open, a wide variety of applications will appear, as will cheaper and faster phones.
But Google's model for Android has some critics. The LiMo Foundation, which publishes specifications for middleware for mobile Linux devices, and of which Google is not a member, says that Google's model might be too open.
"There's a debate about whether Google's approach to openness is sustainable and good for the industry," said Andrew Shikiar, director of global marketing for the LiMo Foundation.
Android will be released under the Apache licence, which doesn't require developers to share their changes to the code back with the community, he said. This is one of the reasons why some people wonder whether Android will become fragmented as various incompatible versions of the software appear in phones across the market.
In the FAQ section of the site for the Open Handset Alliance, the group supporting Android, Google says that using the Apache licence will let manufacturers innovate on the platform and allow them to keep those innovations proprietary as a way to differentiate their offerings.
Shikiar floats a more sinister reason that he's heard for why Google may have chosen the Apache licence. "If it's fragmented and scattered, and the only common version is the Google-optimised one, it's good for the Google," he said. That's because the G1, which is optimised by Google, comes loaded with many Google services that can eventually bring in revenue for the search giant. If that turns out to be the best version of an Android phone, more people will use it and so, presumably, more people will be using Google apps.
Next page: More criticism for Google