The Progress in International Reading Literacy Study (PIRLS) is an educational research study on children's reading literacy achievement conducted in countries and jurisdictions around the world. The first study was conducted in 35 countries during 2001. Administered every five years, the study is designed to measure trends in the achievement of middle primary school students as well as providing countries and jurisdictions with a snapshot of achievement at each cycle. The study involves New Zealand's Year 5 students.

As well as assessing students, PIRLS also collects background information, using questionnaires, from the students, their parents/caregivers, their reading teachers, and from the principals of the schools at which they attend.

The fourth cycle of PIRLS, known internationally as PIRLS 2016, was implemented in New Zealand and other Southern Hemisphere countries in late 2015. Northern Hemisphere countries conducted it in early 2016, so it is often referred to as PIRLS 2015/2016 in New Zealand. Just over 50 countries and education systems around the world participated. The international results were released in December 2017.

Development work for the fifth cycle, PIRLS 2021, is underway, with the field trial and the main study scheduled for implementation in New Zealand in 2020.

PIRLS is conducted under the auspices of the International Association for the Evaluation of Educational Achievement (IEA), which is an independent international co-operative of national research institutions and government agencies. The Ministry of Education's Education Measurement and Assessment Unit manages the implementation of international studies, including PIRLS, in New Zealand.