The T-64 was the direct successor to the venerable T-54/55 series (both designed by Alexander Morozov) and was a significant improvement over the T-62, being the first design designated as a main battle tank by Soviet authorities. The T-64 borrowed the traditional hull and turret layout of Soviet Cold War tanks but featured numerous innovations and structural differences such as smaller-diamater road wheels. One was the incorporation of composite armor known as 'Combination K'. This was composed of two outer layers of steel with a middle layer of glass-reinforced plastic. The T-64 was the first tank in the world to use composite armor which gave it a considerable edge in protection against its NATO contemporaries and also helped keep weight low. Another armor innovation was the introduction of fold-out 'gill' skirts intended to prematurely detonate HEAT rounds, though the effectiveness was questionable and were eventually replaced by standard rubber side skirts. Armament consisted of a 125-mm D-81T smoothbore gun, which was rushed into service due to fears of earlier Soviet tanks being outgunned by the new British L7 gun which became the NATO standard in the 1960s. It was also seen as necessary to penetrate the improved armor of tanks like the M60 and Chieftain. A further novelty was the incorporation of a carousel autoloader which reduced the crew to just three, although the need to stow ammunition under the turret crew was a major vulnerability (one which was inherited by all subsequent Soviet/Russian tanks). Later versions were also able to fire ATGMs from the gun, a feature which has since become standard on Soviet and Russian tanks. Unfortunately, the sophistication of the T-64 was such that it became too expensive to build in mass numbers, to this was added an excessively complex engine, unreliable suspension, and an autoloader that was dangerous to crews. As a result, the T-64 was used primarily to equip elite Red Army units such as the Group of Soviet Forces stationed in East Germany (GSFG) that would have formed the front line against any attack on NATO while the T-62 equipped motor rifle divisions and the subsequent (cheaper) T-72 used for lower category tank divisions. The tank’s expense also meant that it became the only post-WW2 Soviet tank not to be exported, even to its Warsaw Pact allies, although Belarus, Uzbekistan and Ukraine were left with former Soviet stocks after the dissolution of the USSR. Modernized Ukrainian T-64s have seen considerable action in the Donbas in 2014 and during the Russian invasion of 2022, being the most widely available tanks in the country's inventory. It is estimated that around 300 were lost in the battles against separatist and Russian forces in 2014-15 although their performance after the 2022 invasion has been much better thanks to vastly improved training and tactics, with just over 500 lost by the end of 2024 despite much higher intensity of combat. Large losses among Russia's newer tanks have also forced it to deploy T-64s in storage to the front lines as well, with nearly 100 lost during this period.

The original T-64 (Ob’yekt 432) was fitted with the D-68 115-mm gun of the T-62, however, this was quickly switched to the larger caliber D-81T in the T-64A which was the first mass produced variant and which also featured an improved suspension as well as gill armor skirts. The next major variant was the T-64B, with upgraded armor and fire control systems as well as the 2A46M-1 gun which introduced the ability to fire 9K112 (AT-8) missiles. The gill skirts were also replaced by full-length rubber side skirts a few years after the T-64B was introduced and additional armor was added to the glacis plate in the mid-1980s as well. A simpler version without the new FCS or ATGM capability was known as the T-64B1 while the T-64BM had more powerful 1,000-hp engines. The T-64BV introduced Kontakt-1 ERA on the glacis plate, hull sides, and turret and was the most advanced variant of the T-64 at the end of the Cold War. Command variants included the T-64AK, T-64BK, and T-64B1K. The BREM-64 armored recovery vehicle was also built in small numbers. Further development of the T-64 continued primarily in Ukraine where a modernization program resulted in the T-64U and later T-64BM Bulat, which added more advanced ERA, 9K119 (AT-11) missiles, and upgraded equipment in order to bring it to the standard of the T-84. Financial issues resulted in only a small number modified to this standard, however. More cost-effective improvements to the basic T-64BV led to the T-64BV obr. 2017 which added Nizh ERA as well as improved Ukrainian equipment including night sights and SATNAV, these can be distinguished by the lack of a searchlight. Slat armor has also been added to many T-64BVs in combat after the full-scale Russian invasion in 2022.