The transition from vegetative to reproductive development is marked by the establishment of the floral developmental program in the lateral primordia formed by the shoot apical meristem. This is achieved by the coordinate activation, in these primordia, of a set of genes that regulate floral initiation. The time of this activation is determined by a complex network of loci involved in several pathways that are dependent or independent from environmental conditions. In Arabidopsis, the construction and characterization of double mutants is helping to understand the interactions between loci controlling flowering time and the genes that are required to initiate the process of flower development at the lateral primordia.