Eureka to Person of Interest
4 connections
Eureka
Warehouse 13
Fargo from Eureka visits Warehouse 13 in a crossover episode
The X-Files
On Warehouse 13 Mrs. Frederic and Steve Jinks enter The Library, a secret room in the Vatican. There is a pack of Morley cigarettes on the table
Fringe
Fringe makes reference to The X-Files classification of files.
Person of Interest
In the pilot of Person of Interest John Reese's suspect Diane Hanson has emails numerous characters from Fringe