Get a digital art library, free of charge, and enjoy National’s Gallery publications, such as catalogs of thematic exhibitions, monographs and more.
This is National’s Gallery official app, through which, the user can read or download, in pdf format, the following publications, some of which are out of stock in their printed version:

Unknown Treasures from the National Gallery Collections,
Artists’ Donations to the National Gallery, from 1910 to 2012,
Tribute to Yiannis Moralis,
A Tribute to El Greco for the 400th anniversary of his death,
National Gallery -Alexandros Soutzos Museum. Four Centuries of Greek
Painting.