What the relative superlative does
The relative superlative picks out the one in a group that has a quality the most or the least: the tallest, the cheapest. French adds no -est to the adjective. Instead, the definite article goes in front of plus (most) or moins (least).
The article and the adjective agree with the noun in gender and number: le plus grand, la plus grande, les plus grands, les plus grandes. The word plus or moins never changes.
C'est le plus beau film.
It's the most beautiful film.
C'est la moins chère.
It's the least expensive one.
Ce sont les plus grandes.
Those are the biggest ones.
Where the adjective sits
The adjective keeps its usual position: short, common adjectives like beau, grand and petit come before the noun, most others come after it. When the adjective follows the noun, the article appears twice.
Two patterns
Adjective before the noun
Article + plus / moins + adjective + noun
C'est le plus beau jardin.
It's the most beautiful garden.
Adjective after the noun
Article + noun + article + plus / moins + adjective
C'est le livre le plus intéressant.
It's the most interesting book.
Elle porte la robe la moins chère.
She's wearing the least expensive dress.
The group with de
To name the group you stand out in, French uses de, never dans: the tallest in the family is le plus grand de la famille. With le and les, de merges into du and des.
C'est le plus grand de la famille.
He's the tallest in the family.
Paris est la plus belle ville du monde.
Paris is the most beautiful city in the world.
C'est le film le plus long de l'année.
It's the longest film of the year.
The superlative of adverbs
Adverbs have a superlative too: le plus or le moins + adverb. Adverbs never change, so the article is always le, never la or les.
Elle court le plus vite.
She runs the fastest.
C'est Paul qui arrive le plus tôt.
Paul is the one who arrives the earliest.
C'est lui qui appelle le moins souvent.
He's the one who calls the least often.
