Migrating from PHP 4 to PHP 5.0.x

• What has changed in PHP 5.0.x
• Backward Incompatible Changes
• CLI and CGI
• Migrating Configuration Files
• New Functions
• New Directives
• Databases
• New Object Model
• Error Reporting

See also the migration guides for PHP versions 5.1.x, 5.2.x, 5.3.x, 5.4.x, 5.5.x and 5.6.x.