Fiats portfolio would grow considerably in 1958, and offer a large span of horsepower output, with the introduction of the 200, 300, 400 and 500 series tractors.
 
The 400 series is consideres by many to be Fiats first proper "utility" tractor. Due to its size, features and power output, one machine could do every job on a medium size farm.
And being 2/3 the price of its nearest competitors, the 400 series became an instant succes for Fiat, selling 1.800 tractors in its first year. 
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Out of Fiats four series of tractors at the time, the 400 was the only series offered as a tricycle.
The 400 series would later have an orchard (421R), vineyard (431R) and high-crop version (481R) added to the range.
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The machine adopted the well known stressed chassis design, with the engines cast-iron crankcase being part of the tractors backbone. Though more expensive than a subframe design, it would be more durable and easy to maintain.
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The gearbox was a simple but easy to use six forward and two reverse, and had PTO and differentiel-locking on the rear axle as standard.
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Fiats new three-point hitch system named "Control-Matic" was introduced on the 300, 400 and 500 series, and was inspired by the revolutionary three point hitch system with draft control, developed and patented by Harry Ferguson in 1926.
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Apart from the 411RB, all 400 series tractors used a four cylinder, water-cooled, pre-chamber diesel engine of 2.270 cc, capable of 41 hp at 2.300 rpm, and 137 Nm at 1.600 rpm.
The 411RB used a four cylinder, water-cooled, petrol engine of 1.901 cc, capable of 39 hp at 2.500 rpm.
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The diesel engine did share a common problem with most indirect injection diesel engines of the time, being difficult to start in cold weather. The 400 series would need a long time to warm up its glowplugs and prechamper, for it to start successfully. But this seemed to be the only complaint from costumers.
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The Fiat 400 series lasted till 1964, where it became part of Fiats new and streamlined "Diamond-series" of tractor models, and was renamed the 415.
From 1958 to 1969 the Fiat 400-series/415 ended selling 17.000 wheeled and 13.000 crawler tractors.