The National Aeronautics and Space Administration (NASA) Landsat program has been dedicated to sustaining data continuity over the 20-year period during which Landsat Thematic Mapper (TM) and Enhanced TM Plus (ETM+) sensors have been acquiring images of the Earth's surface. In 2000, NASA launched the Earth Observing-1 (EO-1) Advanced Land Imager (ALI) to test new technology that could improve the TM/ETM+ sensor series, yet ensure Landsat data continuity. The study reported here quantified the continuity of satellite-retrieved surface reflectance (ρ) for the three most recent Landsat sensors (Landsat-4 TM, Landsat-5 TM, and Landsat-7 ETM+) and the EO-1 ALI sensor. The study was based on ground-data verification and, in the case of the ETM+ to ALI comparison, coincident image analysis. Reflectance retrieved from all four sensors showed good correlation with ground-measured reflectance, and the sensor-to-sensor data continuity was excellent for all sensors and all bands. A qualitative analysis of the new ALI spectral bands (4p: 0.845-0.890 μm and 5p: 1.20-1.30 μm) showed that ALI band 5p provided information that was different from that provided by the ETM+/ALI shortwave infrared bands 5 and 7 for agricultural targets and that ALI band 4p has the advantage over the existing ETM+ near-infrared (NIR) band 4 and ALI NIR band 4 of being relatively insensitive to water vapor absorption. The basic conclusion of this study is that the four sensors can provide excellent data continuity for temporal studies of natural resources. Furthermore, the new technologies put forward by the EO-1 ALI sensor have had no apparent effect on data continuity and should be considered for the upcoming Landsat-8 sensor payload.