The Workload Management System (WMS) is responsible for distributing and managing tasks across computing and storage resources available on a Grid. WMS assigns user jobs to CEs and SEs belonging to a Grid environment in a convenient fashion, so that:

- jobs are always executed on resources that match the job requirements

- grid-wide load balance is maintained, i.e. jobs are evenly and efficiently distributed across the entire Grid.

The WMS receives requests of job execution from a client, finds the required appropriate resources, then dispatches the requests and follows them until completion.This is done handling failure in between and whenever possible. Other than single batch-like jobs, compound job types handled by the WMS are Directed Acyclic Graphs (a set of jobs where the input/output/execution of one of more jobs may depend on one or more other jobs), Parametric Jobs (multiple jobs with one parametrized description), and Collections (multiple jobs with a common description). Jobs are described via a flexible, high-level Job Definition Language (JDL). As a global grid resource broker, the WMS represents a reliable and efficient entry point to high-end services available on a Grid, providing a common front-end for user job submission.