I consider the language and library extensions listed here as "major" because they fundamentally affect the way you program in C++.

• Exception handling provides a structured way of dealing with errors and "exceptional" conditions
• namespace provides a way to avoid global name clashes between libraries and independent parts of your programs
• Runtime Type Identification provides dynamic "safe" casts and additional information about polymorphic types
• The Standard Template Library provides generic algorithms and containers held together by iterators "generic pointers" - this is a link to Dave Musser's excellent pages on STL
• templates - the core of STL - provide the basic generic types and functions that are being used more and more in C++ these days