The basic MP3 decoding and encoding technology is patent-free in the European Union, all patents having <answer>expired</answer> there. In the United States, the technology will be substantially patent-free on 31 December 2017 (see below). The majority of MP3 patents <answer>expired</answer> in the US between 2007 and 2015.
What happened to the patents that caused them to be patent-free?
expired