This painting was the right half of a decorative panel which Vuillard cut in half and reworked during 1935 (the other half of this painting, 'La Terrasse at Vasouy, the Garden', is also in the Gallery).
Included among the luncheon party are many members of literary and artistic Paris at the time. From left to right are Pierre Bonnard, Madame Alice Schopfer and Monsieur Jean Schopfer (the playwright known as Claude Anet), the novelist Romain Coolus, Misia Natanson, Lucy Hessel, Madame 'Bob' Schopfer and Monsieur Louis Schopfer and the writer Tristan Bernard.
Lucy Hessel actually replaced the earlier figures of Léon and Lise Blum; Vuillard also added her collie dog Basto in the bottom right hand corner.
From The National Gallery Podcast: Episode Fifty, December 2010