The evolution of the adjustable stomatal pore was one of the most significant events in the development of life on land. Mechanisms for stomatal opening enable plants to acquire CO2 for photosynthesis and growth in aerial tissues protected by a thick cuticle. When open, stomata also allow loss of water via transpiration into the atmosphere, thus mechanisms for stomatal closure enable plants to balance CO2 acquisition with preventing excessive water loss to avoid dehydration when water is limited. We know most about the genes that control stomatal aperture from angiosperms, where key genetic pathways actively regulate guard cell turgor by mechanisms including the activation or deactivation of ion channels in response to signals including dehydration, light and circadian rhythms. Stomata are present in diverse land plant lineages, which last shared a common ancestor over 460 million years ago. I will present recent work from our group investigating the mechanisms controlling stomatal movements in diverse land plants, including biosynthesis/signalling of the drought hormone abscisic acid, guard cell ion channels, light responses and circadian rhythms, and what clues we have about their evolutionary history.