This document describes the ICOS specifications for atmosphere stations, which typically consist of a set of integrated analyzers that reside in a shelter with an air intake system that collects air on a mast. The document groups the main atmospheric specification into: measurement set up (chap. 2), measurement protocols (chap. 3), calibration and standards (chap. 4), data management (chap. 5) and quality management (chap. 6). The atmosphere Monitoring Station Assembly (MSA) meets regularly (at least once a year) to mainly review, among other things, the stations performance over the past year and discuss recent development and instrument evaluation.