The complexity of quantum chromodynamics in the non-perturbative domain forces physicist to resort to models in order to describe the phenomena of intermediate energy physics and hence this book develops three different quark models to study light and some heavy mesons: a non relativistic quark model with one-gluon-exchange potential(OGEP) and Instanton-Induced Interaction (III); a semi-relativistic quark model with OGEP and III where the confinement of the quark is modeled with the relativistic harmonic model; a relativistic model where the features of the two previous models are supplemented with the introduction of gluon confinement and thus confined one-gluon-exchange potential (COGEP). Both tensor and spin-orbit parts of the interactions are taken into account in all the three models. It begins with an introduction to the quark model of hadrons covering the SU(3) symmetry in chapter 1 and it discusses in detail the constituent quark models in chapter 2. The three models and a description on decays are developed in chapters 3 and 4. The results and conclusions are presented in chapters 5 and 6. This book predicts mass spectra and certain decays of light and some heavy mesons.