That Most Important Thing: Love (original French title: L'important c'est d'aimer) is a French film directed by Polish filmmaker Andrzej Żuławski. It tells the story of a passionate love relationship between Nadine Chevalier, a B-List actress (Romy Schneider), and Servais Mont, a photographer (Fabio Testi), in the violent and unforgiving French show business.

After Żuławski's second film, The Devil, was banned in Poland, he decided to move to France, where he made this film in 1975. He coadapted and directed it based on the novel by Christopher Frank La Nuit américaine (unrelated to the 1973 François Truffaut film of that name). The success in France was such – it was featuring the very popular actress Romy Schneider and French singer Jacques Dutronc – that it allowed Żuławski to return to Poland. The film had a total of 1,544,986 admissions in France.

Romy Schneider received the inaugural César Award for Best Actress for this role and Pedro Almodóvar dedicated his film All About My Mother partially to her in this role.