Sukhoi-Gulfstream S-21 was a projected Russian-American supersonic business jet.

In the early 1990s, Gulfstream Aerospace and the Sukhoi Design Bureau began a joint effort to develop a supersonic small business jet, code named the S-21.

Due to questionable market demand for commercial supersonic air travel, commitment to the project weakened and delays mounted.

[1] Gulfstream eventually dissolved the partnership, although Sukhoi continued work on the S-21.

As of 2012, the project had not received any funding for the 2013-2025 development period and appeared to be cancelled.