This chapter introduces the computational tools used throughout the book to perform numerical calculations. We begin with an overview of natural units commonly used in particle physics and demonstrate how to convert between different unit systems. A brief introduction to the CERN ROOT library illustrates how to generate random numbers, visualize numerical distributions, and randomly sample an arbitrary function using the rejection sampling algorithm. We also show how to use ROOT’s built-in numerical integration routines with simple one- and two-dimensional functions and how a simple Monte Carlo integration works. The GSL library is introduced for solving ordinary differential equations (ODEs) in both the real and complex domains. Finally, we provide a short overview of ROOT’s built-in physical and mathematical constants, along with references to other well-known publicly available online databases.