The international Network for the Detection of Atmospheric Composition Change (NDACC) began official network operations in January 1991. Today it is composed of more than 110 globally distributed, ground-based, remote-sensing stations with more than 160 currently active instruments. The overriding goal of NDACC is to collect and maintain high-quality data for achieving the following scientific objectives:

• establishing long-term databases for the characterization of the state and behaviour of the atmosphere
• establishing links and feedbacks between changes in atmospheric composition, climate, and air quality
• validating atmospheric measurements from other platforms
• providing critical datasets to fill gaps in satellite observations
• collaboratively supporting field campaigns and other observing networks
• providing validation and development support for atmospheric models
• contributing to assessments of the state of the atmosphere (WMO, IPCC, etc.)

To achieve its objectives, NDACC collaborates with 10 cooperating networks, satellite teams, and model developers.

This special Issue marks the 35th anniversary of NDACC (https://ndacc.org). Its purpose is to present past scientific achievements and to inform readers about the updated strategy of the network in light of the evolution of the scientific questions regarding the state and behaviour of the atmosphere by taking advantage of the current landscape of observations. We also welcome papers that focus on related studies with important implications for our understanding of the state and behaviour of the atmosphere.

The introductory paper to the special issue provides an overview of NDACC's revised strategy for the next decade.