Marc Dormey

If you use Agile as project management methodology then you must have heard of the ‘SOLID’ principles. Agile and SOLID goes hand in hand.
Uncle Bob has a great article on SOLID and explains each principle in detail with examples.

A summary of the principles below:

• S – Single Responsibility Pattern
  A class should have one, and only one, reason to change
• O – Open/Close Principle
  Classes should be closed for modification, but open for extension
• L – Liskov Substitution Principle
  Derived classes must be substitutable for their base classes.
• I – Interface Segregation Principle
  Clients should not be forced to depend upon interfaces that they do not use.
• D – Dependency Inversion Principle
  Depend on abstractions, not concretions

You can read the full article here