The Unidata network Common Data Form (netCDF) is an interface for scientific data access and a freely-distributed software library that provides an implementation of the interface. The netCDF library also defines a machine-independent format for representing scientific data. Together, the interface, library, and format support the creation, access, and sharing of scientific data. The current netCDF software provides C interfaces for applications and data. Separate software distributions available from Unidata provide Java, Fortran, Python, and C++ interfaces. They have been tested on various common platforms. NetCDF files are self-describing, network-transparent, directly accessible, and extendible. Self-describing means that a netCDF file includes information about the data it contains. Network-transparent means that a netCDF file is represented in a form that can be accessed by computers with different ways of storing integers, characters, and floating-point numbers. Direct-access means that a small subset of a large dataset may be accessed efficiently, without first reading through all the preceding data. Extendible means that data can be appended to a netCDF dataset without copying it or redefining its structure.