The ESL tiers is a system used by the United States Department of State (USDS) to rank the English language proficiency of foreign nationals. The tiers range from 1 to 5, with 1 being the lowest and 5 being the highest.
ESL tiers are used by the USDS to determine whether or not a foreign national is eligible for certain visas, such as the F-1 student visa. The required ESL tier for a particular visa will vary depending on the visa category. For example, the F-1 student visa requires a minimum ESL tier of 3, while the B-2 tourist visa does not require any specific ESL tier.