The words tu and vous both mean you. In English, the word you can be used to address any person or number of people, whatever the age, social status etc of that person. In French, which word for you is used depends on the person being addressed (spoken/written to).

A common misconception is that "tu is used for talking to children and vous for talking to adults" or "tu is for friends and vous is for strangers". If this was the whole truth, life would be nice and simple and we could all go away and have a cup of tea rather than reading web pages about when to use tu and when to use vous (and I wouldn't have to write one...). As we'll see below, the reality is a bit more complex. For example, there are situations where two adults meeting for the first time will automatically use tu, and cases where an adult will address a child as vous.

So what can we make of this complex situation? Well, remember first that tu is always used to address a single person. As a general rule of thumb:

The tu form is more likely to be used to address somebody in a similar social situation.

So what does similar social situation mean? Well, all sorts of things-- I've chosen a deliberately vague term. But things like:

So the choice of tu or vous has to do with age, but also to do with other things, and age isn't always the presiding factor.

Linguists sometimes use the term honorific to denote 'polite' forms of language like vous. More generally, tu is often referred to as the familiar form, and vous as the formal or polite form.

Here are some more concrete examples. Note that some of them do refer to age, and that particular ages should of course be taken as 'rough figures'.

Speakers | Form of address used | Comments |

Family members | tu | Family members pretty automatically use tu between one another. So a 3-year-old child would normally use tu tu his 80-year-old grandmother.
Speakers aged 15-30 | Generally tu | Generally, adults up to the age of about 30 (and often up to 40) automatically use tu unless another factor (e.g. a junior worker talking to their boss) provokes vous. Conversely, close solidarity (a 20-year-old and 50-year-old in the same job) could extend this age range.
Adult to child | Often tu unless a specific social barrier demands vous. | Generally, somebody above the age of about 15 would automatically use tu to somebody below the age of 15. For speakers around the age of 15, this is essentially an extension of the previous observation.
Young child to adult | vous | A young child (up to about 10) talking to an adult (aged about 15 onwards) would commonly use vous.
Child to child | tu | Children under the age of about 15 will automatically use tu to one another.
Colleagues | Generally tu, or vous when there is a marked difference in hierarchy | Generally, colleagues would use tu to one another. But, for example, a teacher talking to the headmaster, or a junior office worker talking to their boss or somebody important in the company, would be likely to use vous. It would also be normal for the boss to use vous back to the junior colleague. Particular workplaces can also have particular protocols (just as in English-speaking companies there may be a protocol as to whether people are addressed on first name terms).
Pupil to teacher | vous | This is an analoguous situation to the 'hierarchy gap' mentioned above.
Teacher to primary school pupil | tu | To young children in any social situation, tu is generally used.
Teacher to older pupil | Often vous | It is not uncommon for teachers to use vous to pupils from the age of about 13, possibly as a way of 'distancing themselves' socially from the pupil.
Participants in on-line forums, Internet Relay Chat etc | Generally tu | The tendancy to use tu in these non face-to-face situations appears to be stronger than in face-to-face situations.
New business contacts | vous initially, then often tu | New contacts meeting or exchanging e-mails for the first time would generally use vous. If a close working relationship was forged, then it would be common for one party to suggest using tu.
Speaker A treating speaker B with contempt (e.g. because B has just crashed into A's car). | Often tu | When a speaker wants to be deliberately disrespectful to somebody (e.g. because they're annoyed with them), they can deliberately 'break' the social barrier and use tu where vous would otherwise be expected.

As a general trend, it is more and more common for tu to be used 'automatically', particularly by younger speakers.

Other uses of tu

Speakers use tu when addressing non-humans (speaking to their dog, shouting at their computer...). Christians also use tu when addressing God (and tu forms are embedded in the French version of the Lord's Prayer).

Addressing more than one person

In general, the choice for addressing more than one person, formally or informally, is restricted to vous. Informally (and to people who as individuals they would address as tu), on can also be used to mean 'you (all)'. So the full form of address system is:

  | Formal | Informal
1 person | vous | tu
> 1 person | vous | vous / on