Arborio is a type of short-grained rice that is popularly used in making risotto. However, if you don't have arborio rice or can't find it in the grocery store, there are several alternatives you can use. One common substitute is Carnaroli rice, which is similar to arborio but has a slightly longer grain. Another option is Vialone Nano rice, which has a creamy texture similar to arborio. Other potential substitutes include sushi rice, pearl barley, and quinoa. Keep in mind that the cooking time and liquid requirements may differ when using these alternatives compared to arborio rice, so make sure to adjust your recipe accordingly.