The OFFICAIR project aimed to describe comfort and indoor air quality (IAQ) in new and retrofitted office buildings in Europe. In France, 21 office buildings participated in this project. In a subsample of five buildings, IAQ measurements and performance tests were carried out to study the relations between IAQ and work performance. Twenty-one compounds were measured (volatile organic compounds, aldehydes, nitrogen dioxide, and ozone) as well as environmental parameters: Carbon dioxide, temperature, and relative humidity, over five days in two different seasons. The occupants in the investigated rooms were invited to participate in two on-line task performance tests: A reaction time test, i.e., the standardized Deary-Liewald test, and a memory test. There were participants in summer and 98 in winter. They also provided self-assessments of the influence of the indoor environment on their productivity. The multilevel linear regression models showed that individual characteristics were the main factors determining performance at work. Indoor air concentrations of xylenes and ozone might influence reaction time during summer. Both in summer and winter, the occupants' satisfaction regarding noise and their perceived ability to control their indoor temperature increased their self-assessed productivity. This work is the first to study the influence of IAQ on performance in real work environments and on the basis of IAQmeasurements. This study was limited to five buildings, but it would be useful to repeat it on a larger scale.