In 2017, Ira Steven Behr announced he had reconvened much of the former cast and crew of Deep Space Nine for a documentary film entitled What We Left Behind. It had a very positive response and surpassed its fundraising goals, and this success led to ground-breaking conversions of Deep Space Nine footage into higher definition, although it caused some delays. A screening version was released in late 2018 in Hollywood, New York and at the Destination Star Trek convention in the UK.[65][66][67]


By February 2017, the documentary was partially finished, with an Indiegogo fundraising page set up to crowdsource the rest of the money needed to complete it. In addition to interviews with cast and crew, the documentary will explore Deep Space Nine's legacy; Behr also reconvened the series' old writers' room to develop a script for the first episode of an imagined eighth season, which will be featured in the film.[68] In 2017, a tentative release date was set for 2018.[69] In the summer of 2018, the makers scheduled special release events starting in October 2018.[66] A version was able to be screened at these special release events at Paramount in Hollywood and some other locations, but a decision was made to delay the media release to increase the number of high-definition conversions.[65][67]


In 2017, a fundraiser for the documentary surpassed its target of nearly $150,000 within a day of going live.[70] It went on to raise over $500,000 by March 2017, almost four times the amount requested.[71] When it concluded it had raised over $631,000 from thousands of donations.[72]


Development of What We Left Behind took extra time due in part to the large amount of material for editing and technical challenges.[73] This includes crafting special effects footage and working with CBS to make high-definition scans.[73] The makers also expanded the amount of footage that is being remastered, and innovated with a 16:9 scan of the original DS9 film.[66]


In August 2018, it was announced the documentary would have original music scored by Star Trek veterans Dennis McCarthy (256 Star Trek episodes scored) and Kevin Kiner (10 Star Trek episodes scored).[66] The documentary's producer is Kai de Mello-Folsom, in consultation with others from the original creative team including Michael Okuda, Jonathan West and Doug Drexler.[74]


It premiered in late 2018 at the following locations:[65]


The strong community support and overall response, as well as the creative team's access to resources to create the high-definition sequences led to a delay to increase the sequences filmed in higher definition for the documentary.[67] Although the screening version was complete and could have been released as-is, a creative decision was made to undertake converting more sequences into high definition.[67] One teaser showed concept art of a Star Trek spacecraft, which appears in the documentary in an animated sequence.[75] The spacecraft design was by John Eaves, who designed many spacecraft in the franchise's television shows and theatrical films.[75]


On May 13, 2019, there was a limited theatrical release.[76] It played at about 800 theaters and grossed over $380,000.[77] The film reviewed various aspects of the series from a perspective of twenty years later, explored a plot for a notional eighth season and included many clips re-scanned from original footage in high definition.[76]


On Rotten Tomatoes, it has an approval rating of 100% based on reviews from nine critics.[78]