A service level agreement (SLA) is a contract between a logistics service provider and a customer that typically measurably determines the services that the logistics service provider will provide. Many logistics service providers make an SLA available to their customers. More recently, logistics departments of large companies have embraced the idea of writing a service level agreement so that services to their customers (users of other services within the company) can be measured, justified, and possibly compared to those of outsourcing network providers. Some core metrics or key performance indicators (PPAs) that can indicate LSLs are as follows: unions also often occur between logistics service providers, i.e. the participation of at least two logistics organisations that are likely to compete with each other.