In the Common Law system judges have the power to create subsidiary laws: they make rules in strict sense. This Kind of power responds to a special way in which the Common Law develops and adapts itself to achieve the best rules for a given society. Understanding how the Australian law system works, as an example of a common law structure, and how judges interact with the parliament in the creation of the best rules of law -which makes the process coherent- is paramount for other legal systems that have a mixture of legal institutions from both civil and common law systems, as Colombia. Colombia has an unclear mixture of law systems, which generates an uncertainty of the application of the law producing both by judges and parliament, and serious structural law problems; so, understanding the basis of the common law system it is important to clarify the limits in the competence of each authority and the interaction between the law made by the Parliament and the one that the judges produce.