Boron neutron capture therapy(BNCT) is based on the nuclear reaction of two essentially nontoxic species, boron-10(10B) and thermal neutrons, that yields very high linear energy transfer(LET) particles, α-particles and recoiling lithium-7 nuclei, with a limited path length(5 - 9μm) in tissue so that their destructive effects are limited to boron containing cells. Two boron compounds, sodium mercaptoundecahydrododecaborate(BSH) and p-boronophenylalanine(BPA), have been clinically utilized for the treatment of patients with malignant brain tumors, malignant melanoma, and head and neck cancer. Recently, BNCT has been applied a wide variety of cancers including lung cancer, hepatoma, chest wall cancer, and mesothelioma. Therefore, the development of boron delivery agents for BNCT is an ongoing task that constitutes a crucial issue for the effective application of this therapeutic technology. In the last decade, boron carrier development has taken two directions:small boron molecules and boron-conjugated biological complexes. Unlike approaches using pharmaceuticals, boron carriers require high tumor selectivity and should be essentially non-toxic. In this review, the historical development and current status of boron delivery agents are summarized.