The Interagency Language Roundtable scale is a set of descriptions of abilities to communicate in a language. It was originally developed by the Interagency Language Roundtable (ILR), which included representation by United States Foreign Service Institute, the predecessor of the National Foreign Affairs Training Center (NFATC). It consists of descriptions of five levels of language proficiency, and is the standard grading scale for language proficiency in the Federal service.
ILR Level 1 – Elementary proficiency 
This is the first and essential level of the scale, often called S-1 or Level 1. The following describes the traits of an ILR Level 1 individual:
- can fulfill travelling needs and conduct themselves in a polite manner
- able to use questions and answers for simple topics within a limited level of experience
- able to understand basic questions and speech, which allows for guides, such as slower speech or repetition, to aid understanding
- has only a vocabulary large enough to communicate the most basic of needs; also makes frequent punctuation and grammatical mistakes in writing of the language
- The majority of individuals classified as S-1 are able to perform most basic functions using the language. This includes buying goods, reading the time, ordering simple meals and asking for minimal directions.
ILR Level 2 – Limited working proficiency 
Limited working proficiency is the second level in the scale. This level is sometimes referred to as S-2 or level 2. A person at this level is described as follows:
- able to satisfy routine social demands and limited work requirements
- can handle with confidence most basic social situations including introductions and casual conversations about current events, work, family, and autobiographical information
- can handle limited work requirements, needing help in handling any complications or difficulties; can get the gist of most conversations on non-technical subjects (i.e. topics which require no specialized knowledge), and has a speaking vocabulary sufficient to respond simply with some circumlocutions
- has an accent which, though often quite faulty, is intelligible
- can usually handle elementary constructions quite accurately but does not have thorough or confident control of the grammar.
ILR Level 3 – Professional working proficiency 
Professional working proficiency is the third level in the scale. This level is sometimes referred to as S-3 or Level 3. S-3 is what is usually used to measure how many people in the world know a given language. A person at this level is described as follows:
- able to speak the language with sufficient structural accuracy and vocabulary to participate effectively in most conversations on practical, social, and professional topics
- can discuss particular interests and special fields of competence with reasonable ease
- has comprehension which is quite complete for a normal rate of speech
- has a general vocabulary which is broad enough that he or she rarely has to grope for a word
- has an accent which may be obviously foreign; has a good control of grammar; and whose errors virtually never interfere with understanding and rarely disturb the native speaker.
ILR Level 4 – Full professional proficiency 
Full professional proficiency is the fourth level in the scale. This level is sometimes referred to as S-4 or level 4. A person at this level is described as follows:
- able to use the language fluently and accurately on all levels and as normally pertinent to professional needs.
- can understand and participate in any conversations within the range of own personal and professional experience with a high degree of fluency and precision of vocabulary
- would rarely be taken for a native speaker, but can respond appropriately even in unfamiliar grounds or situations
- makes only quite rare and minute errors of pronunciation and grammar
- can handle informal interpreting of the language.
ILR Level 5 – Native or bilingual proficiency 
Native or bilingual proficiency is the fifth level in the scale. This level is sometimes referred to as S-5 or level 5. A person at this level is described as follows:
- has a speaking proficiency equivalent to that of an educated native speaker
- has complete fluency in the language, such that speech on all levels is fully accepted by educated native speakers in all of its features, including breadth of vocabulary and idiom, colloquialisms, and pertinent cultural references.
See also 
- Common European Framework of Reference for Languages (The European language proficiency scale.)
- Interagency Language Roundtable
- Defense Language Proficiency Tests
- Wikipedia:Babel (originating at Commons:Babel) is a similar, though informal, 0–5 language scale