Active Directory has proven itself as a robust directory service in Windows Server 2003 R2. Windows Server 2008 builds on the prior success of Active Directory with several new and improved features: (courtesy of Microsoft)

Active Directory Domain Services
Active Directory Domain Services (AD DS), formerly known as Active Directory Directory Services, is the central location for configuration information, authentication requests, and information about all of the objects that are stored within your forest. Using Active Directory, you can efficiently manage users, computers, groups, printers, applications, and other directory-enabled objects from one secure, centralized location. Enhancements to AD DS in Windows Server 2008 include:
• Auditing. Changes made to Active Directory objects can be recorded so that you know what was changed on the object, as well as the previous and current values for the changed attributes.
• Fine-Grained Passwords. Password policies can be configured for distinct groups within the domain. No longer does every account have to use the same password policy within the domain.
• Read-Only Domain Controller. A domain controller with a read-only version of the Active Directory database can be deployed in environments where the security of the domain controller cannot be guaranteed, such as branch offices where the physical security of the domain controller is in question, or domain controllers that host additional roles, requiring other users to log on and maintain the server. The use of Read-Only Domain Controllers (RODCs) prevents changes made at branch locations from potentially polluting or corrupting your AD forest via replication. RODCs also eliminate the need to use a staging site for branch office domain controllers, or to send installation media and a domain administrator to the branch location.
• Restartable Active Directory Domain Services. Active Directory Domain Services can be stopped and maintained. Rebooting the domain controller and restarting it in Directory Services Restore Mode is not required for most maintenance functions. Other services on the domain controller can continue functioning while the directory service is offline.
• Database Mounting Tool. A snapshot of the Active Directory database can be mounted using this tool. This allows a domain administrator to view the objects within the snapshot to determine the restore requirements when necessary.

Active Directory Lightweight Directory Services
Active Directory Lightweight Directory Service (AD LDS), formerly known as Active Directory Application Mode, can be used to provide directory services for directory-enabled applications. Instead of using your organization’s AD DS database to store the directory-enabled application data, AD LDS can be used to store the data. AD LDS can be used in conjunction with AD DS so that you can have a central location for security accounts (AD DS) and another location to support the application configuration and directory data (AD LDS). Using AD LDS, you can reduce the overhead associated with Active Directory replication, you do not have to extend the Active Directory schema to support the application, and you can partition the directory structure so that the AD LDS service is only deployed to the servers that need to support the directory-enabled application. Enhancements to AD LDS in Windows Server 2008 include:
• Install from Media Generation. The ability to create installation media for AD LDS by using Ntdsutil.exe or Dsdbutil.exe.
• Auditing. Auditing of changed values within the directory service.
• Database Mounting Tool. Gives you the ability to view data within snapshots of the database files.
• Active Directory Sites and Services Support. Gives you the ability to use Active Directory Sites and Services to manage the replication of the AD LDS data changes.
• Dynamic List of LDIF files. With this feature, you can associate custom LDIF files with the existing default LDIF files used for setup of AD LDS on a server.
• Recursive Linked-Attribute Queries. LDAP queries can follow nested attribute links to determine additional attribute properties, such as group memberships.

Active Directory Certificate Services
Most organizations use certificates to prove the identity of users or computers, as well as to encrypt data during transmission across unsecured network connections. Active Directory Certificate Services (AD CS) enhances security by binding the identity of a person, device, or service to their own private key. Storing the certificate and private key within Active Directory helps securely protect the identity, and Active Directory becomes the centralized location for retrieving the appropriate information when an application places a request. Enhancements to AD CS in Windows Server 2008 include:
• Enrollment Agent Templates. Delegated enrollment agents can be assigned on a per-template basis.
• Integrated Simple Certificate Enrollment Protocol (SCEP). Certificates can be issued to network devices, such as routers.
• Online Responder. Certificate Revocation List (CRL) entries can be returned to the requestor as a single certificate response instead of the entire CRL. This reduces the total amount of network traffic consumed when clients validate certificates.
• Enterprise PKI (PKI View). A new management tool for AD CS, this tool allows a Certificate Services administrator to manage Certification Authority (CA) hierarchies to determine the overall health of the CAs and to easily troubleshoot errors.

Active Directory Federation Services
Active Directory Federation Services is a highly secure, highly extensible, and Internet-scalable identity access solution that allows organizations to authenticate users from partner organizations. Using AD FS in Windows Server 2008, you can simply and very securely grant external users access to your organization’s domain resources. AD FS can also simplify integration between untrusted resources and domain resources within your own organization. Enhancements to AD FS in Windows Server 2008 include:
• Availability As an Integrated Server Role. AD FS is a server role within Windows Server 2008 that can be easily deployed and managed using Server Manager, instead of handled as an added feature, as in Windows Server 2003 R2.
• Integration with Microsoft Office SharePoint Server 2007. AD FS can be used to facilitate a single sign-on solution for Office SharePoint Server 2007.
• Integration with Active Directory Rights ManagementServices (AD RMS). AD FS can integrate with AD RMS to support the sharing of rights-protected content between organizations without requiring AD RMS to be deployed in both organizations.
• Improved Administration. Importing and exporting trust information has been enhanced so that each organization can quickly export or import XML files to facilitate the configuration of trust information.

Active Directory Rights Management Services
Your organization’s intellectual property needs to be safe and highly secure. Active Directory Rights Management Services, a component of Windows Server 2008, is available to help make sure that only those individuals who need to view a file can do so. AD RMS can protect a file by identifying the rights that a user has to the file. Rights can be configured to allow a user to open, modify, print, forward, or take other actions with the rights-managed information. With AD RMS, you can now safeguard data when it is distributed outside of your network. Enhancements of AD RMS in Windows Server 2008 include:
• Application Support. Support for AD RMS is already included within Windows Vista. Internet Explorer 7 and the 2007 Microsoft Office system already have support for AD RMS. The AD RMS client can also be installed on other Windows operating systems.
• Persistent Protection. Your content can be protected on the go. You specify who can open, modify, print, or manage the content, and the rights stay with the content—even after it has been transferred outside of your organization.
• Usage Policy Templates. If you have a common set of rights that you use to control access to information, a Usage Policy Template can be created and applied to content. This alleviates the need to recreate the usage rights settings for every file you want to protect.
• AD RMS Software Development Kit. The AD RMS Software Development Kit (SDK) can be used by independent software vendors (ISVs) to rights-enable their applications, meaning the application investments you’ve already made may be (or will become) compatible with AD RMS.