The papacy’s long-standing entanglements with the twin disciplines of astronomy and astrology can be summarized along three thematic strands. One revolves around the ecclesiastical calendar and the astronomical exigencies of the reckoning of Easter, whose historical ramifications range from late antique Easter controversies to the Gregorian reform of the calendar (1582) and the beginnings of the Vatican Observatory. Another is the more general role of popes as patrons of astronomical research as well as their more anomalous involvement in scientific censorship during the cosmological controversies of the early modern period, as exemplified by the trial against Galileo Galilei (1616/33). A third is the complex relationship between the Roman Curia and astrology, which includes episodes of patronage as much as instances of sharp anti-divinatory legislation, with the latter culminating in the trial against Orazio Morandi (1630).