Kinematics plays a central role in the study of heavy-ion collisions, providing the framework for analyzing particle production, momentum distributions, and the global dynamics of nuclear matter under extreme conditions. In this chapter, the concepts of rapidity, pseudorapidity, transverse momentum, and transverse mass are systematically developed to describe particle production dynamics. The use of Lorentz transformations ensures a consistent treatment of observables across different frames, particularly between the center-of-mass (collider) and laboratory systems (fixed target). Special emphasis is placed on the role of rapidity as a natural variable in relativistic kinematics, its connection with velocity addition, and its utility in characterizing multihadron production dynamics. Applications to experimental observables, including spectra and scaling variables like Feynman-x, demonstrate how kinematical formulations provide direct insight into the physics of strongly interacting matter at high energies. The chapter underscores that a deep understanding of relativistic kinematics is essential for interpreting data from heavy-ion experiments at RHIC, LHC, and future facilities. Plenty of practical examples alongside the kinematic variables used in the search for Quark-Gluon Plasma make this chapter the most sought-after one for the practitioners of high-energy nuclear physics.