“Let’s call it The Blacklist. That sounds exciting. That’s why we're all here, of course. My wish list. A list I’ve been cultivating for over twenty years; politicians, mobsters, hackers, spies. I’m talking about the criminals who matter. Ones you can’t find because you don’t even know they exist. Zamani was a small fish. I’m Ahab. And if you want the whales on my list, you have to play by my rules.” -- Raymond Reddington (“Pilot”)
"The Blacklist" is a list of criminals that Raymond Reddington has compiled in his illegal business dealings. Names on the list are criminals that the FBI does not have overwhelming evidence against, hence why they have never been caught. Some criminals, such as the Kingmaker, are unknown to the FBI. Some, such as Nathaniel Wolff, have avoided leaving behind the needed evidence for conviction. Others like Madeline Pratt live a high profile public life whilst concealing their criminal behaviour.
The list is truly international, with at least 1 member from Russia (Ivan), the People's Republic of China (Wujing), Japan (Mako Tanida), Serbia (Pavlovich brothers) and the UK (Kingmaker), in addition to those from the USA.
According to a list in "The Blacklist (Comic)", the list contains 161 names. This is later shown as 192 names. According to a behind the scenes special for season 4, there will be 200 blacklisters.
In "Smokey Putnum" Red tells Cooper that the Blacklist changes constantly as yesterday's criminals cease being a threat, today's criminals are a threat, and tomorrow's criminals are an unknown possible threat.
In "The Cook" it is shown that Red will add people to the Blacklist in order to obtain the services of another person.
In "Abraham Stern" Red adds a person to the Blacklist so the FBI will indirectly aid his black market activities.