The Patek Philippe reference 3940 is widely regarded as one of the most important perpetual calendar wristwatches of the modern era, marking the beginning of a new chapter for the manufacture's complicated watchmaking. Introduced in 1985 under the leadership of Philippe Stern, the 3940 helped re-establish the perpetual calendar as the flagship complication of Patek Philippe following the quartz crisis. Powered by the ultra-thin automatic Calibre 240 Q, featuring a micro-rotor construction, the watch displays the day, date, month, leap year, 24-hour indication and moon phase in a beautifully balanced arrangement that has become one of the most iconic perpetual calendar layouts in horology.

Produced over more than two decades in yellow gold, white gold, rose gold and platinum, the reference 3940 underwent several subtle evolutions, commonly referred to by collectors as the First, Second and Third Series, each with distinctive dial, case and movement characteristics. Admired for its elegant 36mm proportions, exceptional finishing and enduring mechanical sophistication, the 3940 is considered one of Patek Philippe's greatest modern classics and remains one of the most sought-after perpetual calendar references ever produced.