Technical Abstract: We compared the flight behavior of Lygus hesperus Knight and Lygus lineolaris (Palisot de Beauvois) relative to age, sex, and time of day using tethered (flight mills) and untethered flight (vertical flight chamber) assays. Both species and sexes initiated flights throughout the day, and flight mill assays recorded flights throughout the night. For both species and flight systems, most flights were less than 5 min in duration, with longer flights occurring from 1 to 3 wk of age. Number of flights and flight duration were influenced by age and sex for tethered individuals and by sex for untethered individuals. Species differences were less apparent, but tethered L. lineolaris had more sustained flights that were of longer cumulative duration compared with L. hesperus. The longest flights were obtained with flight mills and were 17 to 18 times longer than the longest flight (22 min) in the flight chamber. Determination of flight periodicity, throughout the day and night, was only possible for tethered insects, and females exhibited more distinct periodicities for sustained flights than males. For L. hesperus females, sustained flights followed a diurnal to crepuscular periodicity, while sustained flights by L. lineolaris females were nocturnal. No significant correlations were found between egg load and any of the flight parameters when grouped by species, but there was a positive correlation between the number of sperm sacks and several of the flight parameters for female L. hesperus. In the vertical flight chamber, takeoffs occurred at low light levels, and were always higher for L. lineolaris than L. hesperus. Rates of climb toward the skylight cue were about 50 cm/s indicating a capacity for strong, self-directed flight by both species.