Star Trek Next Gen/DS9 crossovers?

Question

How many times does the Next Gen storyline cross over with that of DS9? And how significant are those crossovers to either storyline, if any?

Answer 1

The biggest storyline crossover that isn't character-specific is probably the Maquis:

• The first hints that something bad might come up later was in TNG 4x12, The Wounded, where we learn that the Cardassians had in the past sought to expand into Federation space, and relations along the border are still tense.
• Federation colonists were permitted to continue living in their colonies under Cardassian jurisdiction in TNG 7x20, Journey's End.
• The Maquis formed in DS9 2x20/21, The Maquis, Part I and Part II to deal with Cardassian subterfuge that the Federation was not (or could not legally) deal with.
• The Maquis eventually grew strong enough to outright attack the Cardassians, such as in TNG 7x24, Preemptive Strike.
  • This is also the final appearance of Ro Laren, a Bajoran who writers wanted to move over to Deep Space Nine. When the actress declined the role, the character was modified and replaced with Kira Nerys.
• Thomas Riker joins the Maquis at some point between his creation in TNG 6x24, Second Chances and appearance in DS9 3x09, Defiant.
• One Maquis cell ended up in the Delta Quadrant and joined with the USS Voyager to get back home.
• The Maquis made various additional appearances in DS9 before their destruction in DS9 5x15, By Inferno's Light. Only a few isolated cells remained, which were for the most part captured and imprisoned.

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Another that's less "story arc" and more "background" is the Cardassian Occupation of Bajor in general. We're first introduced to it through Ro Laren in TNG 5x03, Ensign Ro, where we learn that Cardassia annexed Bajor 40 years prior, and the Bajorans have since resorted to terrorism to regain their freedom. Come DS9, that freedom has been won and Kira Nerys was rather proud of being one of those terrorists/freedom fighters.

DS9 was set up so that all of this background is reintroduced early on, hence why it's not so much a story arc.

Answer 2

Deep Space Nine episodes with The Next Generation characters:

• S01E01 "Emissary" - recap of Borg battle at Wolf 359 which occurred in TNG's "Best of Both Worlds", Picard, O'Brien from NCC-1701D.

• S01E02 "Past Prologue" - Lursa and B'Etor from the House of Duras, introduced in TNG's "Redemption" return. Also Keiko O'Brien makes her first appearance on DS9 having been introduced in TNG's "In Theory".

• S1E06 "Q-Less" - Vash, introduced in TNG's "Captain's Holiday" and Q, introduced in TNG's "Encounter at Farpoint" return.

• S1E17 "The Forsaken" - Lwaxana Troi, introduced in TNG's "Haven" returns. Also in S03E10 "Fascination" and S04E21 "The Muse".

• S03E01 "The Search (part 1)" - Admiral Nechayev, introduced in TNG's "Chain of Command" returns. Also in S03E02 "The Search (part 2)".

• S03E09 "Defiant" - Thomas Riker, introduced in TNG's "Second Chances" returns.

• S04E01 "The Way Of The Warrior" - Worf from TNG returns and remains until the end of the series.

• S04E15 "Sons Of Mogh" - Kurn, introduced in TNG's "Sins of the Father" returns.

• S05E01 "Apocalypse Rising" - Gowron, introduced in TNG's "Reunion" returns.

• S06E03 "Sons and Daughters" - Alexander Rozhenko, introduced in TNG's "Reunion" as Worf's son, returns as a young adult.

The Next Generation episodes with Deep Space Nine characters:

• S06E16 "Birthright (part 1)" - Bashir interacts with Data and Geordi on Enterprise while Crusher and Picard visit DS9.

• S07E21 "First Born" - Riker has Worf contact Quark on DS9.