Quel (m,sing.) / quelle (f,sing.) / quels (m,pl.) / quelles (f,pl.) = what (e.g. "Quel est votre profession?" – "What is your profession?") Lequel (m,sing.) / Laquelle (f,sing.) / lesquels (m,pl.) / lesquelles (f,pl.) = which (one) (e.g."Je veux le livre là-bas." "Lequel veux-tu?" – "I want the book over there." "Which (one) do you want?") Lequel / Laquelle / lesquels / lesquelles can also be relative pronouns (e.g. "Le livre dans lequel j'ai écrit..." – "The book in which I wrote...")

Merci