Russian troops on the Western Front

Russian soldiers in France

In the early days of WW1, there were stories circulating in Britain that thousands of Imperial Russian troops, including Cossacks, in heavy winter coats and still with snow on their boots had been seen travelling across Britain to the channel ports.  This, of course, was not the case.  It was an inspired piece of propaganda created by the British war office to confuse and misdirect the enemy (two German divisions were rushed from the battle of Marne to defend the Belgian coast), and also to inspire the population of the UK.
However, Russian troops did serve on the Western front.  The Russian Expeditionary Force was sent to France by the Tsar in 1916.
France had originally asked Russia for 300,000 men to be sent.  This was an enormous number, probably based on Russia's insistence that it had unlimited supplies.  Eventually, five brigades were sent to the west, mostly to France, but also to the Salonika Front in northern Greece, totalling around 45,000 men.  A further three divisions would have been sent had it not been for the Russian Revolution of 1917.

Revolution
All five brigades served with distinction, until the confusion of the Russian Revolution and the withdrawal of Russia from the Allies.  One of the camps where the Russian troops were stationed mutinied.  Russian soldiers from an adjacent camp attacked the mutineers, subduing the uprising.  The survivors were initially jailed before being sent back to Russia.

Post-revolution
The Russian troops who had stayed loyal to the Allied cause demanded that they be allowed to continue to fight in spite of the chaos in their home country and their new government's armistice with Germany.  As a result, the Russian Legion was formed which fought within the framework of the 1st Moroccan Infantry Division.  These men fought until the ceasefire of 1918 when the Russian Legion was disbanded and they either stayed in France or returned to what was by then, the Soviet Union.