Genes in the FLOWERING LOCUS T (FT) and TERMINAL FLOWER 1 (TFL1) family have been shown to be important in the control of the switch between vegetative and reproductive growth in several plant species. We isolated nine members of the FT/TFL1 family from Lombardy poplar (Populus nigra var. italica Koehne). Sequence analysis of the members of the FT/TFL1 family revealed considerable homology within their coding regions both among family members and to the members of the same family in Arabidopsis, tomato and grapevine. Moreover, members of this family in all four species examined display a common exon-intron organization. Phylogenetic analysis revealed that the genes fall into four different clades: two into the TFL1 clade; five into the FT clade; and one each into the MOTHER OF FT AND TFL1 and BROTHER OF FT AND TFL1 clades. One gene in the TFL1 clade, PnTFL1, is expressed in vegetative meristems, and transgenic Arabidopsis that ectopically expressed PnTFL1 had a late-flowering phenotype. The expression patterns of two genes in the FT clade, PnFT1 and PnFT2, suggested a role for them in the promotion of flowering, and transgenic Arabidopsis that ectopically expressed either PnFT1 or PnFT2 had an early-flowering phenotype.