This data set contains flight data from Loon, a Google project and later an Alphabet subsidiary that provided wireless internet access to rural areas using high-altitude balloons. The data set includes GPS and sensor data from all 2,131 flights across the project's entire nine-and-a-half year history, from the first sounding balloon experiment in August, 2011, through the last balloon landing in May, 2021. In total the data set comprises over 218 flight-years of data (over 127 million telemetry points), the vast majority from altitudes between 50 and 110 hPa (approximately 15.5 to 21 km above sea level). Please see README.md within the dataset for more details.