Relativistic dynamics extends Newtonian mechanics to regimes where velocities approach the speed of light, ensuring consistency with the principles of special relativity. This chapter develops the formalism starting from the limitations of classical momentum and energy, leading to the introduction of relativistic momentum, relativistic mass, and the energy-momentum relation. The equivalence of mass and energy, encapsulated in the celebrated relation \(\mathrm {E}=\mathrm {mc}^{2}\) is derived, and its profound physical implications are discussed. We then discuss the Lorentz transformation properties of energy and momentum. By combining conceptual clarity with practical examples, the chapter provides a rigorous framework for understanding how energy, momentum, and mass behave in the relativistic domain, forming the basis of modern high-energy physics. A classical correspondence at the low-speed limit is always shown explicitly to give a realistic feeling to the beginners about the importance of the special theory of relativity.