Paul Thomas Anderson got the initial idea for the film while he was sick in bed one day. His wife, Maya Rudolph, was tending to him and gave him a look that made him realize that she had not looked at him with such tenderness and love in a long time.
Director Paul Thomas Anderson said his favorite line in the film was "The tea is going out; the interruption is staying right here with me."
The Spanish fashion designer Cristóbal Balenciaga's relation with his work and the way he led his life, with director Paul Thomas Anderson's words, "monastic life," inspired the character of Reynolds Woodcock.
In preparation for the film, Sir Daniel Day-Lewis watched archival footage of 1940s and 1950s fashion shows, studied famous designers, consulted with the curator of fashion and textiles at the Victoria and Albert Museum in London, and apprenticed under Marc Happel, head of the costume department at the New York City Ballet. He also learned how to sew, and he practiced on his wife Rebecca Miller, trying to recreate a Balenciaga sheath dress that was inspired by a school uniform.
Vicky Krieps did not meet Sir Daniel Day-Lewis until her first day on set. As Day-Lewis famously stays in character during production of his films, Krieps was instructed to refer to him as "Reynolds" for the duration of filming. In multiple interviews promoting the film, Krieps still referred to Day-Lewis as "Reynolds."