Scalar mesons: fifty years of challenging the quark model

Half a century of work on the light scalar mesons $f_0(500)$, $f_0(980)$, $K_0^star(700)$, and $a_0(980)$ is briefly reviewed. After summarising all light scalar candidates in the Review of Particle Physics since 1963, a selection of different theoretical and phenomenological descriptions is presented, including pure meson-meson models, a tetraquark construction, unitarised quark-meson models, unitarised effective chiral approaches, and a very recent lattice-QCD simulation.