The vascular system spreads throughout the plant body. This highly organized network contains several types of cells. Vascular cell development is initiated during embryogenesis, and then vascular cells proliferate, form a vascular pattern, and commit to specific cell fates. Recent molecular genetics and modeling approaches have increased our understanding of the molecular mechanisms underlying early vascular development. Early events during vascular development are tightly linked and controlled by transcriptional complexes consisting of LONESOME HIGHWAY (LHW) and TARGET OF MONOPTEROS5 (TMO5) families. The role of LHW-TMO5 is tightly coupled with biosynthesis and/or signaling of phytohormones such as auxin and cytokinin. In this review, we discuss the regulatory network mediated by LHW-TMO5 during early vascular development.