Gravity waves (GWs) are key drivers of atmospheric dynamics, with major impacts on climate and weather processes. However, they are challenging to measure in observational data, and as a result no large-area multidecadal GW time series yet exist. This has prevented us from quantifying the interactions between GWs and long–timescale climate processes. Here, we exploit temperatures measured by commercial aircraft since 1994 as part of the In-Service Aircraft for a Global Observing System (IAGOS) atmospheric chemistry research program to produce a novel 26-year time series of upper troposphere/lower stratosphere (UTLS) GW measurements across most of the Northern Hemisphere. We analyze 90,342 flight hours (76.2 million flight kilometers) of data, typically at a temporal resolution of seconds and with high temperature precision.We show that GW activity in the Northern Hemisphere UTLS is consistently strongest north of and above the upper tropospheric jet.We also show that GW sources not typically observed in stratospheric data but assumed in model schemes, such as the Rocky Mountains, are visible at these altitudes, suggesting that wave momentum from these sources is deposited specifically between ∼200 and 50 hPa. Our data show no significant impact of the Quasi-Biennial Oscillation, the Northern Annular Mode, or climate change. However, we do see strong evidence of links with the El Niño–Southern Oscillation, which modulates the measured GW signal by 25%, and weak evidence of links with the 11-year solar cycle. These results have important implications for atmospheric process modeling and for understanding large-scale climate teleconnections.