The High Level Architecture (HLA) is a general purpose architecture for distributed computer simulation systems. It is defined under IEEE Standard 1516:

• IEEE 1516-2000 - Standard for Modeling and Simulation High Level Architecture - Framework and Rules
• IEEE 1516.1-2000 - Standard for Modeling and Simulation High Level Architecture - Federate Interface Specification
• IEEE 1516.1-2000 Errata (2003-oct-16)
• IEEE 1516.2-2000 - Standard for Modeling and Simulation High Level Architecture - Object Model Template (OMT) Specification
• IEEE 1516.3-2003 - Recommended Practice for High Level Architecture Federation Development and Execution Process (FEDEP)

Another important document is this one:

• Department of Defense (DoD) Interpretations of the IEEE 1516-2000 series of standards, Release 2 (2003-jul-01)

To implement the HLA a Runtime infrastructure (RTI) is needed.

HLA (in both the current IEEE 1516 version and its ancestor "1.3" version) is the subject of the NATO draft standardization agreement (STANAG 4603) for modelling and simulation: Modelling And Simulation Architecture Standards For Technical Interoperability: High Level Architecture (HLA).