What are the three ways to ask a question in French?

First, intonation: take a statement and raise the pitch at the end - 'tu viens?' (are you coming?). This is the default in spoken French. Second, est-ce que: bolt 'est-ce que' onto the start of a statement - 'est-ce que tu viens?'. This works in any register and is the safest learner move. Third, inversion: flip the subject and verb with a hyphen - 'viens-tu?'. This is formal and used mostly in writing or careful speech. All three are correct; pick by register.

What is the difference between qui and que in French questions?

Qui asks about people: 'qui parle?' (who is speaking?), 'qui as-tu vu?' (who did you see?). Que (or quoi after a preposition) asks about things: 'que fais-tu?' (what are you doing?), 'qu'est-ce que c'est?' (what is it?). The split is based on whether the answer is a person (qui) or a thing (que/quoi). In casual speech, 'quoi' often replaces 'que' even in subject position - 'tu fais quoi?' for 'what are you doing?'.

French Question Words

French has eight question words you'll use constantly, plus three strategies for turning a statement into a question. This page covers both.

The eight question words

Word	Meaning	Example
qui	who	Qui parle?
que	what	Que fais-tu?
quoi	what (after prep)	C'est quoi? / Avec quoi?
quand	when	Quand pars-tu?
ou	where	Ou habites-tu?
comment	how	Comment vas-tu?
combien	how much / many	Combien ca coute?
pourquoi	why	Pourquoi tu ris?

Plus the determiner quel / quelle / quels / quelles (which / what), which agrees with the noun.

Quel livre? (Which book?)
Quelle heure est-il? (What time is it?)
Quels sont tes plans? (What are your plans?)

The three question-formation strategies

For any question, French gives you three options. They're ranked by register.

1. Intonation (casual)

Take the statement and raise the pitch at the end. Word order doesn't change.

Tu viens? (Are you coming?)
Vous habitez ici? (Do you live here?)
Marie est francaise? (Is Marie French?)

With a question word, the word usually goes at the end:

Tu pars quand? (When are you leaving?)
Vous habitez ou? (Where do you live?)
Tu fais quoi? (What are you doing?)

This is the default register for spoken French. It's grammatical, common, and what you'll hear most.

2. est-ce que (neutral)

Bolt est-ce que onto the start of the statement. The rest of the sentence stays the same.

Est-ce que tu viens? (Are you coming?)
Est-ce que vous habitez ici? (Do you live here?)
Est-ce que Marie est francaise? (Is Marie French?)

With a question word, the question word goes first:

Quand est-ce que tu pars? (When are you leaving?)
Ou est-ce que vous habitez? (Where do you live?)
Pourquoi est-ce que tu ris? (Why are you laughing?)

This is the safest learner move. It works in any register, you can't get the word order wrong, and it's never inappropriate.

3. Inversion (formal)

Flip the subject and verb, joining them with a hyphen.

Viens-tu? (Are you coming?)
Habitez-vous ici? (Do you live here?)
Est-elle francaise? (Is she French?)

With a third-person verb ending in a vowel and a vowel-starting pronoun, French inserts a -t- between them for pronunciation:

A-t-il un chien? (Does he have a dog?)
Va-t-elle au cinema? (Is she going to the cinema?)
Parle-t-on francais ici? (Do they speak French here?)

This is the formal register: written French, careful speech, public-facing communication. In conversation it can sound stiff.

qui vs que vs quoi

The three "what / who" words split by function.

qui = who, asking about a person, in any position
que = what, asking about a thing, in subject or object position with a verb directly after
quoi = what, used after a preposition or at the end of a sentence

Examples:

Qui parle? (Who is speaking?)
Qui as-tu vu? (Who did you see?)
Que fais-tu? (What are you doing?)
Qu'est-ce que c'est? (What is it?)
Avec quoi? (With what?)
A quoi penses-tu? (What are you thinking about?)

In casual speech, quoi also creeps into positions that would formally take que: tu fais quoi? for "what are you doing?" is universal in conversation.

Yes / no questions

For yes / no questions (no question word), the three strategies become:

Strategy	Example
Intonation	Tu viens?
est-ce que	Est-ce que tu viens?
Inversion	Viens-tu?

All three mean "Are you coming?". Register differs, meaning doesn't.

Worked examples

Comment t'appelles-tu? (What's your name? - formal)
Tu t'appelles comment? (What's your name? - casual)
Quand est-ce que vous partez en vacances? (When are you going on holiday?)
Pourquoi tu ne reponds pas? (Why aren't you answering?)
Quelle est ta couleur preferee? (What's your favourite colour?)
Combien coute ce livre? (How much does this book cost?)
A qui parles-tu? (Who are you talking to?)

Common mistakes English speakers make

Translating "do you...?" with a French auxiliary - there isn't one. Faites-vous... is the inversion of the main verb, not a French "do". Mixing the three strategies: writing est-ce que viens-tu mashes est-ce que and inversion together, which is wrong. Forgetting the -t- insertion in third-person inversion: a il un chien? is wrong, it's a-t-il un chien?. And translating "what" as quoi in subject position - quoi fais-tu? is wrong, it's que fais-tu? or qu'est-ce que tu fais? in writing.