Film distributor TOHO announced that Studio Ghibli’s next film will be an adaptation of Joan G. Robinson's British children's novel classic When Marnie Was There, according to Variety.
When Marnie Was There (Omoide no Marnie)  is planned for next summer, and will be directed by Hiromasa Yonebayashi, who also directed 2010’s The Secret World of Arrietty.  The screenplay is written by Keiko Niwa (Ocean Waves, From Up On Poppy Hill, The Secret World of Arrietty), Masashi Ando (character designer on Princess Mononoke, Spirited Away, Paprika), and Yonebayashi.
Robinson’s book was first published by (Harper) Collins in 1967, and was last printed by HarperCollins Children’s Books in 2002, though it is currently out of print.  
The story involves young orphan Anna, who lives with foster parents and has no friends. When she moves in with the Peggs, she spends her time amongst the sand dunes around the water.  She meets a strange girl named Marnie who becomes her first friend.  Then one day Marnie vanishes.
The novel is on a list of 50 recommended children’s books Hayao Miyazaki created for an art exhibit in 2011.  Miyazaki announced his retirement from feature films after The Wind Rises, his 11th film, back in September (see "Miyazaki Is Retiring" and "'The Wind Rises' Trailer").