There are 4 books by Gillian O'Brien on BookOrb. A strong starting point is Blood runs green (2015). The bibliography below is in publication order, with series grouped in reading order.
Standalone books
Frequently asked questions
How many books has Gillian O'Brien written?
BookOrb lists 4 books by Gillian O'Brien.
Where should I start with Gillian O'Brien?
A good starting point is Blood runs green (2015).
What is the Gillian O'Brien books in order list?
In publication order: 1. History and environment (1998), 2. Portraits of the city (2012), 3. Blood runs green (2015), 4. Darkness Echoing (2020).