In French, "h" is never pronounced like English /h/. It’s always inaudible… but it can have an effect!

The « h aspiré » is a phenomenon where a word starts with a zero phoneme. Basically, you have to pretend it starts with a consonant even though you don’t hear anything.

Why is that important? Because consonants affect how words run together.

For example, words that start with consonants don’t allow elision. Neither does a word that starts with an « h aspiré » :

l’orange mais le pays (orange starts with a vowel but pays starts with a consonant)

l’homme mais le héros (homme has an « h muet » but héros has an « h aspiré »)

Words that start with consonants also don’t allow liaison. Neither does a word that starts with an « h aspiré » :

cet orange mais ce pays

cet homme mais ce héros

There are other similar alternations, but hopefully these examples make the pattern clear.

How do you tell whether a word has an « h aspiré » or an « h muet » ?

The Wikipedia article lists some ideas, though nothing is failsafe and most are hard to do on the fly. For example, it says that Germanic words tend to have an « h aspiré » while Latinate words have an « h muet ». But how do you know which words are Germanic if you’re not a linguist?

The failsafe way is to check a dictionary (as usual), where it will be marked in the pronunciation.

For example, here’s the WordReference pronunciation for homme with its « h muet ». Notice how the first symbol is a vowel:

/ɔm/

But here’s the pronunciation for « héros » with its « h aspiré ». Notice that the first symbol is an apostrophe:

/ˈeʀo/

In addition to Luke answer which clearly explains the h aspiré issue, note that despite the fact the letter “h” is never pronounced and thus that there is no [h] consonant listed in the phonetic French alphabet, the sound [h] can nevertheless be heard in spoken French without relationship between the presence or not of the letter “h”, especially at the beginning of sentences with a stressed first vowel.

For example, the sentence:

Et alors ?

is sometimes pronounced with a leading [h], he alɔʁ instead of e alɔʁ

We make no distinction between the variants.

That also explain why the French accent often mix up words like “and ” and “hand“, “to heat” and “to eat“…