Title: Phosphine in the Atmosphere of Venus: Now you see it - now you don't Abstract: The presence of phosphine (PH3) in the atmosphere of Venus was reported by Greaves et al. (2021), based on spectroscopy of the J=1-0 transition using the Atacama Large Millimeter/submillimeter Array (ALMA) and the James Clerk Maxwell Telescope (JCMT). This unexpected discovery presents a challenge for our understanding of Venus's atmosphere, and has led to a reappraisal of the possible sources and sinks of PH3, for example, from photochemical, geochemical, meteorological and even biological processes. The claimed detection of PH3, however, was contested by several subsequent, independent analyses of the ALMA and JCMT data, and searches for infrared signatures of PH3 using other ground and space-based instruments have resulted in non-detections. Phosphine on Venus remains a serious topic for discussion in the planetary science community due to its potentially profound implications, and the fact that PH3 was also found in a recent reanalysis of Pioneer Venus mass spectrometry data. In this talk, I will examine the previous ALMA and JCMT detections, and present new results on a sensitive search for PH3 on Venus based on observations made using the GREAT instrument onboard the SOFIA aircraft, over three flights conducted in November 2021.