Were you surprised to learn that only the last act in the chart you just did was a crime? What makes it different from the others? Put simply, a crime is any act- or sometimes a failure to act - that society considers so serious a threat to its safety and well-being that government authorities will prosecute anyone committing it.

The basis of our criminal law system lies in England's common law. The expression common law refers to the decision reached by judges as they tried cases over the centuries. These decisions, as a body, have served historically as precedents on which later judges have based their decisions in similar cases. In this way, a large body of case law (or judge-made law ) has evolved over the centuries, this is known as common law.

Originally there was no real distinction between criminal law and civil law. If someone robbed you, or assaulted you, for instance, it was up to you to bring the suspect before the judge, and the judge's principal concern was to compensate you for your loss rather than to punish the wrongdoer. By the twelfth century, in England, a strong monarchy had emerged and the Crown began to turn its attention to the administration of criminal law. Cases in which the Crown itself was interested were known as 'pleas of the crown' and involved things like trespassing on the monarch's property or committing treason. Gradually the role of the Crown expanded, and the idea developed that any acts of violence within the monarch's domain were public wrongs that should be punished by the state. Hence, criminal law as we know it today, was born.