Plants show remarkable developmental plasticity to survive in a continually changing environment. One example is their capability to adjust flowering time in response to environmental changes. Ambient growth temperature, which is strongly affected by global temperature changes, has a profound effect on flowering time. However, those effects have been largely ignored in research. Recent molecular genetic studies of Arabidopsis as a model system have implicated several genes, and have identified a molecular mechanism underlying the responses of plants to changes in ambient temperature. Here, we describe recent discoveries related to ambient temperature signaling and the control of flowering time in Arabidopsis. We also discuss current perspectives on how plants sense and respond to such changes.