Successful sexual reproduction in plants relies upon the strict coordination of flowering time with favourable seasons of the year. One of the most important seasonal cues for the model plantArabidopsis thaliana(Arabidopsis) is day length. Genes influencing flowering time inArabidopsishave been isolated, some of which are involved in the perception and signalling of day length. This review discusses recent progress that has been made in understanding howArabidopsisintegrates environmental and internal signals to ensure a sharp transition to flowering and new insights on the role of the circadian clock in controlling the expression of genes that promote flowering in response to day length.