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Under certain circumstances, the equations governing magnetic field lines can be reformulated in a canonical form after defining an appropriate field line Hamiltonian. This analogy is particularly valuable for dealing with a variety of problems involving magnetically confined plasmas, like in tokamaks and other toroidal devices,  where a symmetric coordinate often functions as the time variable in the canonical equations. The Hamiltonian formulation for magnetic field lines enables the application of Hamiltonian methods to interpret results and characterize the dynamic regimes observed in both experiments and computational simulations. For instance, explicit area-preserving maps, derived from the Poincaré map of the magnetic field lines, are frequently studied. These Hamiltonian maps inform us about the global and fine scale structure of the edge magnetic topology in toroidal systems. They are essential tools for studying kinetic and fluid transport processes, such as plasma turbulence and MHD stability. In this presentation, we explore how the magnetic field lines represent a non-mechanical system that can be effectively described using Hamiltonian formalism. Starting from the variational principle, we present the description of field lines in confined plasmas for different coordinate systems and with the inclusion of an external perturbation