Plant cells encounter a variety of environmental stimuli, They often respond by a rapid and transient increase in the concentration of cytosolic calcium (Ca2+). These Ca2+ signals modulate cellular processes via high-affinity, Ca2+-binding proteins, such as calmodulin, which in turn regulate the activity of downstream target proteins. In recent years a number of calmodulin-related proteins have been identified that are unique to plants. In addition, plant calmodulins have novel functions not previously described in other organisms, and dynamic expression patterns of calmodulin-related genes modulated by environmental signals.