Seine-et-Oise is a former department of France, which encompassed the western, northern and southern parts of the metropolitan area of Paris. Its prefecture was Versailles and its administrative number was 78. Seine-et-Oise was disbanded in 1968 as part of the reorganisation of the departments of the Paris metropolitan area. The newly-created Yvelines department inherited the 78 number.

Essonne is a department in the southern part of the Île-de-France region in Northern France. It is named after the river Essonne. In 2019, it had a population of 1,301,659, across 194 communes.