The term Tornado Alley is usually given to a certain area from the US which is often visited by tornadoes. This Tornado Alley region spreads over the areas of the  central plains to the Southeast, Mississippi, the lower Missouri River Valleys and Ohio, generally lowland areas.

There are no states which are completely free of tornadoes, but the Great Plains areas are the ones that see them most often. There is a number of factors which conspire to reach this effect, including the fact that the ground is relatively flat, which means that the tropical air coming from the Mexican Gulf can meet with the cold air coming from north, from Canada. The majority of these tornadoes will be formed near the front where the two masses of air meet. There are certain states in the US which are affected most by tornadoes, these states being Missouri, Iowa, Arkansas, Kansas, Oklahoma, Nebraska and Texas. These seven states are the ones that are at the core of Tornado Alley, though areas from Indiana, Illinois, Mississippi, South Dakota, Minnesota, Louisiana, Colorado are also affected.

Thanks to the increased chance of tornadoes, there are many areas that are part of Tornado Alley where there are stricter building codes, at least compared with other areas from the US. There are structures like roofs that need to be strengthened, connections between foundations and buildings which need to be stronger and other things like that, which are designed to make sure that those areas have better protection against tornadoes. Having storm cellars available and adding tornado sirens are other things which are covered by these laws.

Even though tornadoes occur mostly in this area, there are instances where they appeared in other areas in the US, though in southern states they are mostly a result of hurricanes.