We investigated the influence of lunar and environmental factors on behavior of Common Poorwills (Phalaenoptilus nuttallii) in southern Arizona under a diverse set of natural and artificial conditions. Radio-marked poorwills were most active shortly after sunset during the new moon. Movements declined as evening progressed. Activity remained high for several hours after sunset when the moon was full. Poorwills were heard calling from March through October, but most calling occurred between early May and September. Only ambient light was correlated with number of poorwills heard calling. More poorwills responded to playbacks of conspecifics when the moon was full than when it was new. Poorwills did not change their response to conspecifics during full moon when playback of poorwill calls followed playback of Great Horned Owl (Bubo virginianus) calls but, during the new moon, fewer birds responded following the owl call. Poorwill behavior is strongly influenced by lunar conditions; their ability to detect and evade predators is important when calling advertises their location.