Subspace is the medium through which faster-than-light travel and communication is possible, and an integral part of the space-time continuum that co-exists alongside normal space, while being distinct from it. Subspace contains an infinite number of domains and has been compared to a honeycomb with an infinite number of cells. Subspace is home to the Solanae encountered by the U.S.S. Enterprise-D and, possibly, home to the Elachi.
- In 2369, the Solanae secretly abducted numerous crew members from the Enterprise-D and performed experiments on them. They attempted to create a pocket of their native domain by causing an expanding spatial rupture that threatened the ship. The rupture is eventually sealed with a graviton pulse.
- In 2409, the Elachi stage their offensive against the Romulan Republic from a subspace cell. Later the same year, the Solanae-controlled region of subspace is revisited where the Solanae are found to be servants of the Iconians.
The Solanae have resided in subspace for thousands of years as their molecular structure was modified to be comprised of solanogen, a material that can only exist in subspace, following a large scale accident which exposed them to massive amounts of tetryonic energy.
The Elachi are another race active in subspace that serves the Iconians. While it is not known if the Elachi actually originate from subspace, the Elachi operate bases in subspace, including Station Alpha and Subspace Base 002, and use it as a staging ground for their invasion of the Romulan Republic.
- “Preemptive Strike”: The Romulan Star Empire secretly builds subspace weapons on Rator III, intending to use them against Vulcan and the rest of the Federation to avenge the destruction of Romulus.
- “Devil's Choice”: The player uses a captured Elachi S'golth Escort, Target Alpha, to infiltrate a massive Elachi Base hidden in subspace.
- “Sphere of Influence”: The player uses an Iconian gateway to travel to Solanae Storage Facility Z98 in subspace, where the player learns more about the gateways. Several gateways are found to have been hidden in subspace by the Iconians. These gateways are later pushed into normal space when the Gateway network is reset to save New Romulus.
- “Unsafe Practices”: The player learns from a Voth called Nelen Exil that a large scale accident occurred when the Solanae activated the Solanae Dyson Sphere thousands of years ago, prompting the survivors to flee into subspace in order to survive as their molecular structure had been changed by exposure to massive amounts of tetryonic energy.