Maps Liberation and Piazza are available, and will be followed by a third piece of content in February and another two in March. The DLC will then become available to all users as a single map pack.
Activision has launched a new trailer to accompany the DLC and to promote its Call of Duty: Elite service.
Each piece of DLC will first launch on Xbox Live, with availability on PlayStation 3 and PC following at a later time.
Modern Warfare 3 will see a total of 20 updates over a period of nine months.
Call of Duty: Modern Warfare 3 was released in November and has broken Avatar's record as the fastest-selling piece of entertainment, but failed to topple Adele as the UK's best-selling entertainment property in 2011.
> Watch the Content Season trailer for Call of Duty: Modern Warfare 3
View screenshots for Modern Warfare 3 maps Liberation and Piazza below: