Positioned on the leaf epidermis, stomata are microscopic pores that connect the plants inner tissues with the external environment. Through adjustments in aperture and development, stomata regulate the amount of CO2 available for photosynthesis and the water loss by transpiration. Calcium is an important secondary messenger that coordinates multiple stomatal responses. This study, in part, investigated the role of calcium during stomatal development through the action of calmodulin-binding transcriptional activators. CAMTA1 and CAMTA3 appear to play a partial role in regulating epidermal cell fate and the number of developing stomata. The bulk of this study focused on the nuclear localized Ca2+-permeable channel, CNGC15. CNGC15 is responsible for generating nuclear calcium transients during symbioses in the root hairs of Medicago truncatula. This study investigated the role of CNGC15 in Arabidopsis guard cells during stomatal movements and development. The results found CNGC15 to play a fundamental role in ABA-induced stomatal closure and light-induced stomatal opening as well as a partial role in extracellular Ca2+-induced stomatal closure. The fact that the ion channel is involved in both closing and opening pathways suggests a central role for CNGC15 in stomatal signalling. In Medicago root hairs, CNGC15 is regulated by a potassium-permeable ion channel DMI1. Experiments investigated the role of DMI1 in Arabidopsis guard cells and compared to the role of CNGC15. The DMI1 ion channel appears to be functional in light-induced stomatal opening but is not involved in ABA or Ca2+-induced stomatal closure. Therefore, it is concluded that in Arabidopsis CNGC15 is not regulated by DMI1 but rather another mechanism. This study aimed to investigate the role of nuclear calcium signalling in stomatal responses. The work highlights the gene, CNGC15, which appears to be integral in stomatal responses, proposing an additional level of specificity in stomatal calcium dependent signalling via the nucleus.