As regulated in Spanish law, money laundering requires a prior illicit activity that has generated the assets that are the subject of laundering. One of the subjects that has been deeply discussed in recent years by certain doctrinal sectors, even with support in various jurisprudential rulings, has been the suitability of crimes against the Public Treasury, especially tax fraud, as the prior offence underlying money laundering. Thus, it has been debated whether the tax offender carrying out one of the activities typified in the Criminal Code (acquiring, possessing, using, converting or transmitting assets) automatically commits a type of money laundering. In that case, it would become an automatic and inevitable consequence of the tax crime itself. If, on the contrary, some other component must be required (essentially through the subjective elements of the unjust) to determine the existence of a second crime, that of money laundering, the prohibition of non-bis in idem confronts us, to a greater or lesser extent. Furthermore, doctrinal approaches and some judgements of the Spanish highest courts have generated a reinterpretation of the criminal law that fits badly with the principles of criminality. Nor is it easy to delineate the assets that are the object of the tax offence that may be subject to laundering, since, by definition, they are assets that were originally in possession of the offending subject and, besides, they are pecuniary obligations. To that extent, the presumption of innocence could, in many cases, determine the exoneration of the suspect.