Background
Since the discovery of strongly interacting constituents of nuclei nearly 60 years ago, there has been intense interest in non-perturbative approaches for hadrons and their interactions. A vast number of models have been developed in order to describe hadronic bound state spectra and transition rates. The challenge has been to arrive at a similar level of success from a fundamental starting point, the field theory of the strong interactions known as Quantum Chromodynamics (QCD). The requirements of a fully relativistic and non-perturbative approach have been addressed within both Lagrangian and Hamiltonian formulations with some success. Our focus is on the Hamiltonian approach and the application of light-front coordinates which provides a systematic description and permits new insights into the underlying physical phenomena.
Dirac introduced light-front coordinates in 1949 and exhibited many of the conceptual challenges of quantizing with this choice of coordinates. Advantages for field theory applications have appeared over the years and numerous new issues have been uncovered depending on the field theory investigated and/or the approximations invoked. In the past few years there has been a great deal of progress in systematically resolving these issues and improving the methods developed within light-front quantization schemes.