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EPiServer CMS updates its partner list twice a year, and the data we can compile from it shows the CMS' popularity around the world. One thing is the number of partners in each country, but another more interesting metric is the number of certified developers on the EPiServer platform as this is more closely linked to the size of the market share.
The updated list published in January 2012 clearly shows that EPiServer dominates its homeland, Sweden, with 294 ECDs (EPiServer Certified Developers) and its neighbor Norway with 117 ECDs. The biggest partner, Making Waves, is also based in Norway.
EPiServer AB has had a clear goal of expanding into the UK and US market, and we can see the result of this in the growth in ECDs in both countries which now ranks third (45, a growth of 6) and fourth (30, a growth of 10) respectively. And interesting point is the the biggest US partner, First Line Software, is based in Russia.
We can also find partners in Australia, Poland, Serbia, Finland, Netherlands, France etc., but an a glaring omission in that list is Denmark with 0 ECDs. A good guess would be that the Danish .Net CMS, Sitecore, has cornered the market, but I might be mistaken.
To see the summed up stats for the 2012 EPiServer partner list check out this blog post on EPiServer World: http://world.episerver.com/Blogs/Alexander-Haneng/Dates/2012/2/The-Biggest-EPiServer-Partners-Worldwide-2012/