Microsoft made a statement regarding its filing of legal action against Samsung.

We don’t take lightly filing a legal action, especially against a company with which we’ve enjoyed a long and productive partnership. Unfortunately, even partners sometimes disagree. After spending months trying to resolve our disagreement, Samsung has made clear in a series of letters and discussions that we have a fundamental disagreement as to the meaning of our contract.

Samsung and Microsoft are both large and sophisticated companies. In 2011, after months of painstaking negotiation, Samsung voluntarily entered into a legally binding contract with Microsoft to cross-license IP – an agreement which has been extremely beneficial for both parties. Samsung had been complying with the contract and paying to use Microsoft’s IP.

So what changed? Since Samsung entered into the agreement, its smartphone sales have quadrupled and it is now the leading worldwide player in the smartphone market. Consider this: when Samsung entered into the agreement in 2011, it shipped 82 million Android smartphones. Just three years later, it shipped 314 million Android smartphones. [Source: IDC, WW Quarterly Mobile Phone Tracker – 2014 Q1, Published: May 2014] Samsung predicted it would be successful, but no one imagined their Android smartphone sales would increase this much.

After becoming the leading player in the worldwide smartphone market, Samsung decided late last year to stop complying with its agreement with Microsoft.

How much is at stake? Microsoft reportedly makes $2 billion from Android patents.