"Luke Cage" does, of course, refer back to Luke's involvement in the events of "Jessica Jones," but it's pretty oblique for the most part. In the series premiere, Pop (one of the few who know about Luke's secret superpowers) mentions the time Jessica had to shoot Luke in the head with a shotgun.

Turk Bennett was a supporting character in "Daredevil," until the Devil himself shut down Turk's gun dealer operation, at which point Turk, apparently, fled to Harlem and started hanging out at Pop's barbershop.

Claire herself is a unifying element amongst all the Marvel Netflix series thus far, as she has made prominent appearances in "Daredevil," "Jessica Jones" and "Luke Cage."

We learn that part of "Luke Cage" takes place during the second season of "Daredevil" because when Claire Temple makes her first appearance, she references the recent ninja attack on the hospital where she worked in Hell's Kitchen as being the reason she's visiting her mom in Harlem.

In episode 6, we get to hear a part of an episode of "Trish Talk" in which Trish Walker, Jessica Jones' adoptive sister, discusses the public emergence of Luke Cage Harlem. 

When Luke Cage and Diamondback face off in the United Palace Theater in episode 8, Diamondback claims credit for all the misfortune that's befallen Luke, from his imprisonment to the death of his wife Reva. He then admits he was joking about Reva -- which we knew because, in "Jessica Jones," she was killed by Jessica when they were both under Kilgrave's influence.

In "Jessica Jones," Luke and Jessica recover a USB stick that had belonged to Reva. In the ninth episode of "Luke Cage," we discover it has lots of secret files about Luke from his time at Seagate Prison.

In the tenth episode, Mariah gives a speech about the troubles with New York's super-people and mentions Jessica having to kill the mind-controlling villain Kilgrave.

Assistant district attorney Blake Tower played a major role in "Daredevil" Season 2, and he pops up in episode 11 of "Luke Cage" to help Inspector Ridley handle a hostage situation at Harlem's Paradise.

When federal agents come to take Luke back to prison in the finale, Claire Temple says she knows a good lawyer who will take his case to prove his innocence. She's talking about Matt Murdock, aka Daredevil.

In the finale, Claire Temple grabs a phone number off a flyer for self-defense classes. The person giving the classes is none other than Colleen Wing, a skilled martial artist and swordswoman who will appear in the next Netflix Marvel series, "Iron Fist," in 2018.