S - Single Responsibility Principle - One class should be responsible for doing one thing and one thing only and well O - Open Closed Principle - A class should be open for extension but close for modification L - Liskov Substitution Principle - A child class can be replace by a base parent class (I'm shorting the explanation) I - Interface Segregation Principle - A class implementing a interface should be allow to implement what it needs (smaller interfaces) D - Dependency Inversion Principle - Decouple classes, high-level modules should not depend on low-level modules, for example, in Java when we use DI for example for a EJB to obtain a database connection, we just tell the class to grab it from a reference, a container (runtime) will resolve the reference and inject an instance in our EJB so they can be use