The infantry tank was a tank concept developed by the United Kingdom and France in the years leading up to World War II. Infantry tanks were designed to support infantrymen in an attack. To achieve this, the vehicles were generally heavily armoured to allow them to operate in close concert with infantry even under heavy fire. The extra armour came at the expense of speed, which was not an issue when supporting relatively slow-moving foot soldiers.

Once an attack supported by infantry tanks had broken through heavily defended areas in the enemy lines, faster tanks such as cruiser or light tanks were expected to use their higher speed and longer range to operate far behind the front and cut lines of supply and communications.

The infantry tank was superseded by the "Universal Tank" concept which could adequately perform the roles of both infantry and cruiser tank, as represented by the Centurion which replaced both the Churchill and any medium or cruiser tanks then in service. This led to the main battle tank.

The experimental armoured formations of the British army were mostly equipped with the Vickers Medium Tank Mk I and Medium Mk II, which were judged obsolete by the 1930s; most of the vehicles were at the end of their mechanical life. It was impractical to build more because their road speed of only 18 mph (29 km/h) was too slow for manoeuvre warfare and their armament of a 3-pounder gun lacked the power to penetrate newer foreign tanks. By 1931, experience with the Experimental Mechanized Force led to the report of the Kirke Committee and specifications for three types of tank, a medium tank with a small-calibre anti-tank gun and a machine-gun, a light tank armed with machine-guns for reconnaissance and to co-operate with medium tanks by engaging anti-tank guns. A close support tank armed with a gun firing high explosive and smoke shells to give covering fire for tank attacks was also specified. The Wall Street crash of 1929 and the Great Depression led to big reductions in the funds made available for the army. Money spent on tracked vehicles fell from £357,000 in 1931–32 to £301,000 in the year 1932–33 and exceeded the 1931 figure only in 1934–35.

In May 1934, Lieutenant-General Hugh Elles was appointed Master-General of the Ordnance and Brigadier Percy Hobart, the Inspector, Royal Tank Corps, asked Vickers to design a tank for infantry co-operation, that could survive all existing anti-tank weapons and be cheap enough for mass production in peacetime. The next year, Vickers had a two-man tank design, with a machine-gun and powered by a civilian Ford V8 engine of 70 hp (52 kW). The prototype of October 1936 weighted 10 long tons (10 t) had a maximum speed of only 8 mph (13 km/h) but carried 60–65 mm (2.4–2.6 in) of armour and was mechanically reliable. The A11, Infantry Tank Mk I, was the first Infantry tank (I tank) and the first practical expression of the decision to split design into I tanks and cruiser tanks, with different functions and tactics, supplied to separate units and formations.

The 1935 edition of the War Office publication, Field Service Regulations (FSR), containing the principles by which the army was to act to achieve objectives, was written by Major-General Archibald Wavell, made breakthrough the responsibility of infantry divisions with the support of Army Tank Battalions, equipped with specialised vehicles for infantry-artillery co-operation, the slow and heavy Infantry tanks. Once a breakthrough had been created, a Mobile Division containing a tank brigade with light and cruiser tanks, would advance through the gap and use the speed and range of its tanks to surprise the defender and attack flanks, headquarters and non-combatant units. By 1939, further amendments to FSR added counter-attacks on an enemy armoured breakthrough. (The codification of the difference between Infantry and cruiser tanks and their functions in FSR 1935, accidentally created an obstacle to all-arms co-operation that lasted long into the Second World War.) Defence against tanks could be achieved by troops finding physical obstacles and by controlling their own anti-tank guns. The obstacles could be woods and rivers or minefields as long as they were covered by fire from other weapons. In places lacking convenient terrain features, lines-of-communication troops would also need anti-tank guns and be trained to set up localities suitable for all-round defence

The need for economy in the design and production of the A11, which was too small for a radio, led to work on a successor, the A12, Infantry Tank Mk II in 1936. Capable of 15 mph (24 km/h), the A12 was still slow but had 60–70 mm (2.4–2.8 in) of armour, making it almost invulnerable to tank guns and standard foreign guns like the German 37 mm Pak 36 anti-tank gun. The tank had a four-man crew and a turret big enough for a radio and an Ordnance QF 2-pounder high-velocity gun, firing solid projectiles capable of penetrating all 1939–1940 German tanks. Vickers and government factories could not take on the work and it was farmed out to a civilian firm, which lacked experience, designers and draftsmen. It took until 1939 to bring the A12 into production as the "Matilda II" and it had not gone into service when the war began, only 67 A11s having been delivered. When the Matilda was supplied to Army Tank Battalions it was an effective tank in the Battle of France and in the Western Desert Campaign, where it outclassed Italian tanks and was effective against standard Italian and German anti-tank guns from 1940 to 1941 but was later found to be too slow for the fast tempo that German panzer units could achieve and unable to engage the more powerful German anti-tank guns from long range with high explosive shells.

Using later terminology, the infantry tank has been compared to a heavy tank, while the cruisers were compared to mediums, lights, or even armoured cars. This comparison can be misleading; late Second World War heavy tanks were intended to have superior anti-tank capabilities, which wasn't a focus of the traditional infantry tank.