What percentage of devices have each of the Android versions?

We're starting out with some Android development in our company, and I'm working out which Android versions we should support.

In one of Google's videos from 27th May 2010 (22:34 minutes in) there is a pie chart showing roughly a third of users each for Android 1.5, 1.6 and 2.1.

Does anyone have a more up-to-date source for the percentages of active Android devices with each version of the platform?

Answer

Check out Official Android Developer's Dashboards.

Data as of September, 2017 ¹

Version       Codename       Distribution
2.3.3-2.3.7    Gingerbread       0.6%
4.0.3-4.0.4    Ice Cream         0.6%
               Sandwich
4.1.x          Jelly Bean        2.4%

4.2.x                            3.5%
4.3                              1.0%
4.4            KitKat           15.1%
5.0            Lollipop          7.1%
5.1                             21.7%
6.0            Marshmallow      32.2%
7.0            Nougat           14.2%
7.1                              1.6%

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¹ Data collected during a 7-day period ending on September 11, 2016. Any versions with less than 0.1% distribution are not shown. (Note: Beginning in September 2013, devices running versions older than Android 2.3.3 do not appear in this data because those devices do not support the new Google Play Store app. As of August 2013, devices with versions lower than 2.2 accounted for about 1% of all devices.)