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Physical properties of matter are tightly related with the kind of symmetryof the medium. Group theory is a systematic tool, though not always easy tohandle, to exploit symmetry properties, for instance to find the eigenvectorsand eigenvalues of an operator. Certain properties (optical activity,piezoelectricity...) are forbidden in molecules or crystals of high symmetry. Afew theorems (Noether, Goldstone...) establish general relations betweenphysical properties and symmetry. Applications of group theory to condensedmatter physics, elementary particle physics, quantum mechanics,electromagnetism are reviewed. Group theory is not only a tool, but also abeautiful construction which casts insight into natural phenomena.    Les propri\'et\'es de la mati\`ere sont li\'ees au type de sym\'etrie qui yr\`egne. La th\'eorie des groupes est un outil syst\'ematique, mais pastoujours commode, pour exploiter cette sym\'etrie, notamment quand il fauttrouver les vecteurs propres et valeurs propres d'un op\'erateur. Certainespropri\'et\'es (pouvoir rotatoire optique, pi\'ezo\'electricit\'e...) sontinterdites dans des cristaux ou mol\'ecules de haute sym\'etrie. Quelquesth\'eor\`emes (Noether, Goldstone...) \'enoncent des relations g\'en\'eralesentre les propri\'et\'es physiques et la sym\'etrie. On passe en revue quelquesapplications de la th\'eorie des groupes \`a la physique de la mati\`erecondens\'ee, \`a la physique des particules \'el\'ementaires, \`a lam\'ecanique quantique, \`a l'\'electromagn\'etisme. La th\'eorie des groupesn'est pas seulement un outil, mais aussi une belle construction qui permet demieux comprendre la nature.

Sym\'etrie et th\'eorie des groupes \`a travers la physique