NGC 4666 is a spiral galaxy in the equatorial constellation of Virgo, located at a distance of approximately 55 megalight-years from the Milky Way.

[6] John L. E. Dreyer described it as "bright, very large, much extended 45°±, pretty suddenly brighter middle".

[2] The morphological classification of this galaxy is SABc, which indicates a weak bar around the nucleus with moderately wound spiral arms.

[2] This is a starburst galaxy that is noteworthy for its vigorous star formation, which creates an unusual superwind[9] of out-flowing gas.

This wind is not visible at optical wavelengths, but is prominent in X-rays, and has been observed by the ESA XMM-Newton space telescope.