Duology

A duology is a story told in two parts.

See also miniseries for trilogies and multipart stories. And anthology for a collection of stories or omnibus for a reprinted collection of works.

Enterprise

 * Daedalus and Daedalus's Children, by Dave Stern

The Original Series

 * The Yesterday Saga, by A.C. Crispin
 * Worlds Apart, by John M. Ford
 * Fortunes of War, by Diane Carey

The Next Generation

 * Gemworld, by John Vornholt
 * Maximum Warp, by Dave Galanter and Greg Brodeur
 * A Time to Be Born, A Time to Die, by John Vornholt
 * A Time to Sow, A Time to Harvest, by Dayton Ward and Kevin Dilmore
 * A Time to Love, A Time to Hate, by Robert Greenberger
 * ''A Time to Kill, A Time to Heal, by David Mack

Deep Space Nine

 * ''Avatar, by S.D. Perry
 * The Left Hand of Destiny, by J.G. Hertzler and Jeffrey Lang

Voyager

 * Homecoming and The Farther Shore, by Christie Golden
 * Spirit Walk, by Christie Golden

Corps of Engineers

 * Interphase, by Dayton Ward and Kevin Dilmore
 * Invincible, by David Mack & Keith R.A. DeCandido
 * War Stories, by Keith R.A. DeCandido
 * Wildfire, by David Mack
 * Ishtar Rising, by Michael A. Martin and Andy Mangels
 * Collective Hindsight, by Aaron Rosenberg
 * The Demon, by Loren L. Coleman and Randall N. Bills
 * Creative Couplings, by Glenn Hauman and Aaron Rosenberg
 * Wounds, by Ilsa J. Bick
 * Remembrance of Things Past, by Terri Osborne

Crossovers

 * The Badlands, by Susan Wright
 * Dark Passions, by Susan Wright