The two countries have agreed on air traffic measures, but that's as far as the cooperation will go.
The US and its allies remain deeply opposed to Russia's involvement in Syria, which they say is further complicating the conflict.
It's the first - and may be the only - sign of cooperation between the US and Russia as both countries conduct air strikes in Syria.
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The US-led coalition and Russia both claim to be targeting IS fighters, but the US claims Russia is also pursuing its own interests.
US Defense spokesman Peter Cook says the deal is limited to air safety only.
"The discussions through which this MoU was developed do not constitute US cooperation or support for Russia's policy or actions in Syria. In fact, far from it. We continue to believe that Russia's strategy in Syria is counterproductive and their support for the Assad regime will only make Syria's civil war worse."
Russia's deputy Defence Minister, Anatoly Antonov, says Russia sought a more substantial agreement with the US, including the sharing of information about military targets.
He's defending Russia's involvement in the conflict, and says the US-led intervention lacks legitimacy.
"The signing of the document in no way changes the Russian position of principle, whose military forces in Syria are operating at the request of legitimate authorities of that country while projection of force of the United States and the counter-ISIL coalition led by Washington on the territory of Syria without the consent of Damascus and in the absence of relevant UN Security Council resolution represents negligence of the international law."
Russia began bombing in Syria on September the 30th, claiming to be targeting IS.
But the US and Syrian activists say Russia is hitting President Bashar al-Assad's non-IS enemies, the rebel forces opposing his government.
But Russian President Vladimir Putin doesn't differentiate, insisting Russia's campaign is against those he calls "terrorists".
"Having established a foothold in Syria and some other Middle Eastern countries, the terrorists have built, and continue building plans to increase expansion to destabilise entire regions, have recruited and continue to recruit fighters into their ranks from many countries, including - unfortunately - from Russia."
Russia's support of Mr Assad is a point of ongoing tension with the US and its allies.
Britain says Syrian President Bashar al-Assad must go as part of any deal by world powers to end the conflict.
British Foreign Secretary Philip Hammond says Russia's intervention in the four-year conflict is complicating the already-chaotic political and military landscape in Syria.
"Syria is facing a humanitarian crisis as a result of the continued assault by the Assad regime on the civilian population, and the brutal occupation of a significant part of the country by ISIL. The Russian intervention, purportedly to join the fight against ISIL, but in fact targeting principally non-ISIL opposition positions, is complicating the situation and risks driving back much of the opposition into the arms of ISIL."
