Summary
Active Directory provides the core service of identity management. AD DS is the traditional on-premises solution, whereas Microsoft Entra ID is the cloud-based solution. Microsoft Entra ID is frequently adopted at first to facilitate authentication for cloud-based apps, but is capable of providing authentication services for the entire infrastructure. While they provide similar solutions, each offer different capability and are often used together to provide a best-of-breed solution. Microsoft Entra ID is offered as a free service, with paid tiers for additional capabilities, depending on an organization's needs.