Crossover Episodes

Unification, Part 1
Star Trek: The Next Generation
S5 E7 - Unification, Part 1
Unification, Part 2
Star Trek: The Next Generation
S5 E8 - Unification, Part 2
Trials and Tribble-ations
Star Trek: Deep Space Nine
S5 E6 - Trials and Tribble-ations
These Are the Voyages
Star Trek: Enterprise
S4 E22 - These Are the Voyages
Flashback
Star Trek: Voyager
S3 E2 - Flashback
Through the Looking Glass
Star Trek: Deep Space Nine
S3 E19 - Through the Looking Glass
Blood Oath
Star Trek: Deep Space Nine
S2 E19 - Blood Oath
The Forsaken
Star Trek: Deep Space Nine
S1 E17 - The Forsaken
Pathfinder
Star Trek: Voyager
S6 E10 - Pathfinder