From the publisher's website:
World of Tanks is a team-based massively multiplayer online game dedicated to armored warfare in the mid-20th century. Throw yourself into epic tank battles shoulder to shoulder with other steel cowboys to dominate the world with tank supremacy!
An advanced system of vehicle upgrade and development allows you to try out the vehicles and weapons featured in the game. Whether you prefer to exhaust your foes with fast and maneuverable light tanks, punch deep into enemy lines with all-purpose medium tanks, use the power of heavy tanks to eliminate opposing forces, or become a high-powered sniper using long-range artillery, each unit type is extremely lethal and effective when commanded by a true tank ace.
It takes more than just being a great tank commander to win. In World of Tanks, it's all about teamwork. Victory can only be achieved through the combined efforts of every member of the team, each playing their own role on the battlefield.