Ray tracing is a fundamental technique in optical system analysis and design, enabling the modeling of light propagation through lenses, mirrors, and other optical elements. Paraxial ray tracing operates under the small-angle approximation, which assumes that light rays make small angles with the optical axis, simplifying calculations by ignoring higher-order terms. This method is highly effective for preliminary optical system design, offering quick insights into image formation and magnification. However, its limitations become evident when dealing with systems requiring high precision where aberrations and distortions are significant. Exact ray tracing, on the other hand, accounts for the full geometry of light rays without approximations, providing a more accurate representation of real-world optical behavior. It considers all ray intersections and refractions according to Snell’s Law, making it important for designing complex systems such as objective lens, telescopes, microscopes, and cameras. In this chapter we will study the paraxial and exact ray tracing through optical system. We will design few lenses using softwares like Python and Zemax OpticStudio.