The Simple Publishing Interface (SPI) is a new publishing protocol, developed under the auspices of the European Committee for Standardization (CEN) workshop on learning technologies. This protocol aims to facilitate the communication between content producing tools and repositories that persistently manage learning resources and metadata. The SPI work focuses on two problems: (1) facilitating the metadata and resource publication process (publication in this context refers to the ability to ingest metadata and resources); and (2) enabling interoperability between various components in a federation of repositories. This article discusses the different contexts where a protocol for publishing resources is relevant. SPI contains an abstract domain model and presents several methods that a repository can support. An Atom Publishing Protocol binding is proposed that allows for implementing SPI with a concrete technology and enables interoperability between applications.