Windows Server 2019 is available in Essentials, Standard and Datacenter editions. It can be downloaded from the Volume Licensing Service Center by Windows Server licensees with Software Assurance coverage (Software Assurance is an annuity that assures upgrades within a contract period). It's also available for download by testers at Microsoft's Evaluation Center. Those deploying Windows Server 2019 on an Azure virtual machine can access the download from the Azure Marketplace.