Law, as it maintains the Law up to date through a special dynamic wherein proof is the most significant factor. For this reason, it is no exaggeration to affirm that fort purposes of its objectives and ultimate ends, Criminal Law –both in its general and special parts– is entirely conditioned on proof. Otherwise, it would not go beyond theoretical knowledge with no practical relevance. Proof is the fundamental factor upon which all Procedure gravitates; upon it will depend the genesis of the process, its development, and the achievement of its ultimate end. If those that must determine the legal situation of the probable perpetrator of an illegal act or conduct were not to base themselves on the proof in order to support their determination, it would lack the strength necessary to sustain its reasoning – both general and particular. For these reasons, the study of proof is a must; to that end, we will focus on a set of doctrinal and juridical principles related to the essence, activities, objectives and ends that justify its existence in Criminal Procedural Law. Accordingly, it will include the following matters: etymology and concept; historical background; acts that constitute proof and their place in the system of Criminal Procedure. Also, its governing principles, elements of proof, its objectives and results; systems for assessment of the proof; the problems over the so called “burden of proof;” and in particular, the classification and analysis of the methods of proof established in Colombian Law.