French adjectives change to agree in gender and number with the nouns that they modify, which means there can be up to four forms of each adjective. The different forms for adjectives depend mostly on the final letter(s) of the default form of the adjective, which is the masculine singular.
Most French adjectives add E for feminine and S for plural. This rule applies to adjectives that end in most consonants as well as all vowels except the unaccented E. It also includes all regular and most irregular present participles and past participles:
Adjective: vert (green)
Masculine singular vert
Feminine singular verte
Masculine plural verts
Feminine plural vertes
Adjective: bleu (blue)
Masculine singular bleu
Feminine singular bleue
Masculine plural bleus
Feminine plural bleues
Adjective: amusant (funny)
Masculine singular amusant
Feminine singular amusante
Masculine plural amusants
Feminine plural amusantes
Adjective: épicé (spicy)
Masculine singular épicé
Feminine singular épicée
Masculine plural épicés
Feminine plural épicées
When the masculine singular adjective ends in an unaccented E, there is no difference between the masculine and feminine forms:
Adjective: rouge (red)
Masculine singular rouge
Feminine singular rouge
Masculine plural rouges
Feminine plural rouges
When the default form of the adjective ends in S or X, there is no difference between the masculine singular and plural forms:
Adjective: gris (grey)
Masculine singular gris
Feminine singular grise
Masculine plural gris
Feminine plural grises
While most French adjectives fit into one of the above categories, there are still quite a few that have irregular feminine and/or plural forms.
Quiz: Agreement of French adjectives
Note: These rules are the same for making nouns feminine and plural.

