The R package zoo provides an S3 class and methods for indexed totally ordered observations, such as irregular and regular time series. Its key design goals are independence from a particular index class and compatibility with standard R functions, similar to the "ts" class. The package supports a wide range of operations, including plotting, merging, binding, mathematical operations, extracting and replacing data and index, coercion, and NA handling. It also includes a subclass "zooreg" for regular time series, which bridges the gap between regular and irregular time series classes. The "zoo" class can be used directly or as a foundation for other specialized applications. The package supports various index classes, including "Date", "POSIXct", and custom classes like "timeDate" and "yearmon". It provides methods for handling NA values, rolling statistics, and coercion between different time series classes. The package is compatible with other R packages such as strucchange, tseries, and fCalendar, and can be extended with new index classes. The zoo package offers extensive functionality for working with indexed observations and facilitates operations such as NA handling and time series analysis.The R package zoo provides an S3 class and methods for indexed totally ordered observations, such as irregular and regular time series. Its key design goals are independence from a particular index class and compatibility with standard R functions, similar to the "ts" class. The package supports a wide range of operations, including plotting, merging, binding, mathematical operations, extracting and replacing data and index, coercion, and NA handling. It also includes a subclass "zooreg" for regular time series, which bridges the gap between regular and irregular time series classes. The "zoo" class can be used directly or as a foundation for other specialized applications. The package supports various index classes, including "Date", "POSIXct", and custom classes like "timeDate" and "yearmon". It provides methods for handling NA values, rolling statistics, and coercion between different time series classes. The package is compatible with other R packages such as strucchange, tseries, and fCalendar, and can be extended with new index classes. The zoo package offers extensive functionality for working with indexed observations and facilitates operations such as NA handling and time series analysis.