  We write to report the discovery that Deneb is a large amplitude polarization
variable. Over a ~400 d time span from August 2022 Deneb's polarization was
typically around 3900 parts-per-million (ppm) in the SDSS g'-band. Yet, it
varied by several hundred ppm in an irregular way on a timescale of weeks. The
largest polarization change, amounting to 2500 ppm, occurred shortly after the
last pulsation ``resumption'' event identified by Abt et al. (2023) in TESS
photometry. The relationship between the observed polarization -- particularly
corresponding to the resumption event -- and its brightness and H-alpha spectra
suggests a mechanism involving density changes in its wind and/or extended
atmosphere. Smaller effects due to pulsations are not ruled out and further
study is recommended.
