Egner spent 25 years working on the series – consisting of collected literature as well as his own stories and illustrations – and they were published in 1950–1972.
[1] Among the recurring characters was the young boy Ola-Ola, who grew up on a farm on the Norwegian countryside, but later moved to the city and had to adapt to a new life.
Other stories took place in far-away lands, reminiscent of the environment in Egner's celebrated When the Robbers Came to Cardamom Town.
In 1972, however – the year in which the last book in the series was published – the educational program of Norwegian primary schools was altered.
[2] The books remain an important part of the Norwegian cultural heritage, being considered children's classics, and some of them have been reprinted more recently.