The genus Lycopersicon is native to western South America. Mexico appears to have been the site of domestication and the source of the earliest introductions of tomato (Solanum lycopersicum L.; previously named Lycopersicon esculentum Mill.). Likely environmental conditions in its natural habitat are little (25 mm) rainfall, high relative humidity, temperatures ranging from 10 to 24°C and photoperiods ranging from 11.5 to 12.5 hours per day (Cooper 1972). Tomato is a perennial plant usually grown as an annual.There are several excellent reviews on tomato flowering (Wittwer and Aung 1969;Picken et al. 1985;Atherton and Harris 1986;Dieleman and Heuvelink 1992; Kinet and Peet 1997; Lozano et al. 2000;Lifschitz and Eshed 2006). Here our focus will be on the timing of the initial transition to flowering and how environmental conditions affect this timing. Our current knowledge in tomato will be briefly compared to that known in other species, especially Arabidopsis.Unlike most model systems, such as Arabidopsis and rice, in tomato vegetative and reproductive phases alternate regularly along the compound (sympodial) shoots of tomato. The primary vegetative apex is terminated by an inflorescence (Sawhney and Greyson 1972), after 6-12 leaves have formed. As described below, the number of leaves depends on genetic background and on environmental cues. Upward growth then continues from a new vegetative shoot arising from the upper-most (proximal) side (axillary) bud (meristem) of the youngest leaf just below the terminating inflorescence. From then on, the stem is composed of reiterated units, sympodial segments, each with three nodal leaves and a terminal inflorescence. The position of the last leaf formed before the transition appears later on above the inflorescence. This is due to a partial fusion of its petiole with the new vegetative shoot arising from its axillary bud which displaces the inflorescence axis sideways, and places the leaf above it (Figure 1). Lateral branches emerging from axillary buds of other leaves, normally produce more leaves before appearance of the first flower, and are not partially fused to their host leaf petiole. This is an interesting point since although the plant has clearly already gone through a first transition to flowering, new branches do not seem to flower as quickly as sympodial branches (Lifschitz and Eshed 2006).The developmental 'time' of transition can be best measured by counting the number of leaves (or nodes) formed on the initial apical meristem before it is terminated with the production of the first inflorescence. In this review we will not mention conditions or Abstract Tomato (Solanum lycopersicum L.) is a very important commercial crop and also a useful model to study the transition to flowering in a sympodial perennial plant. Here we try and summarize past and recent progress in understanding the environmental cues that affect the initial transition to flowering in this species and the genes that are involved in this transition and additional transitions occurring o...