During the years of practice in the Courts of Justice I have taken a great interest in Criminal Law, I have been an observer of judicial decisions full of justice as well as injustice. This small work is mainly focused on the practice within the oral, public and contradictory trial phase and how the correct application of the Iura Novit Curia and the Principle of Congruence can be determinant at the time of acquitting or convicting a person.