S7 is an R package that implements a new object-oriented programming system intended to succeed S3 and S4. Developed by the R Consortium OOP Working Group, it provides formal class definitions via `new_class()`, a property system with type checking and validation, generic functions with multiple dispatch, method registration, and comprehensive compatibility with S3 and S4. The package includes a C extension for performance-critical dispatch and property access. The architecture is a standard R package with exported API functions, internal helper modules, and extensive test coverage. It is consumed as a dependency by several other packages and is designed to eventually be incorporated into base R. There are no data analysis or research-specific components; the entire repository focuses on language infrastructure for object-oriented programming.