This specification describes a data delivery standard for time series data. It is used within the Heliophysics and Geosciences communities. It offers a very simple interface for serving data and is generic in that it captures the fundamental capabilities offered by many time series data providers. PDF versions of the specification are provided here. The development of the specification is done on GitHub (see the repository link below), where there are also various other software projects for software that leverage the standard for providing data access (server-side support) and that use the standard to assist with data analysis (client side tools).