You can use Active Directory Domains and Trusts to manage domain trusts.

• Understanding Trusts
  
  
• Understanding Trust Types
  
  
• Understanding Trust Direction
  
  
• Understanding Trust Transitivity
  
  
• Understanding When to Create an External Trust
  
  
• Understanding When to Create a Shortcut Trust
  
  
• Understanding When to Create a Realm Trust
  
  
• Create a Shortcut Trust
  
  
• Create an External Trust
  
  
• Create a Realm Trust
  
  
• Verify a Trust
  
  
• Remove a Trust
  
  
• Select the Scope of Authentication for Users