Object-oriented programming (OOP) enables high-level programming, bringing it closer to human reasoning rather than machine functionality. This approach simplifies the maintenance of large-scale software projects, particularly those developed collaboratively. At the core of OOP lies the class concept, which encapsulates data and functions—called methods—designed to process and manipulate information. Conceptually, a class is conceived as a tool to address a specific problem in the most comprehensive and general way possible. A common strategy for solving complex problems is to break them down into smaller, more manageable components. Thus, having multiple classes, each dedicated to solving a different aspect of the problem, aligns perfectly to tackle complex challenges efficiently. This chapter aims to highlight the significance of the OOP paradigm in data analysis, introduce the fundamental properties of classes, and provide guidance on implementing basic examples. While there is extensive literature on best practices for designing classes, such in-depth discussions extend beyond the scope of this book.