Money laundering is a process that people convert their dirty money into legaltimate way , which are mainly earned from illegal channels and business, such as gambling, bootlegging , brothels, and extortion, etc. There have been a notorious criminal called Al Capone who was involved in such business. Capone and his associates had hidden many of his criminal incoming into various investment business.  

However, in his time, there're no such expression like money laundering, even though what he did belonged to the same meaning. Anyway, by then , the authority arrested him by a similar accusation of tax evasion. 

Until 1986, the United States officially treated money laundering as a federal crime . 

As time goes on, the money laundering has been developed into much more types and varies methods, and most of them share three basically steps :  placement , layering , and integration. 

Placement is a way that the illegally funds are transferred into some like legal assets, which is often handled by putting funds into a bank account under an anonymous corporation or a middle man.  This step is pretty much popular during the criminals. 

Layering is much more hidden way to clean these money, which is involved into multiple transactions to further distance funds from their origin. For instance, they will be used to buy much more valuable property like high-priced cars, artwork and real estate, also there're a traditional ways to be venue of layering: casinos. 

Integration is a way to make the money clean while the way can benefit the original criminals. for example : they invest the money into a legal business claiming payment by producing fake invoices. Besides, to held a big charity is also a way to integrate such dirty money. 

Anyway, money laundering is a process to circulate huge funds with dark or convert ways, which is hard to disappear under the desire of people pursuing the big interests in the world.