Hydrogen peroxide (H2O2) is an important commodity chemical and its demand is growing significantly in the chemical synthesis due to its "green" character. Currently, H2O2 is produced almost exclusively by the anthraquinone auto-oxidation (AO) process. The AO process involves indirect oxidation of hydrogen and thus avoids potentially explosive H-2/O-2 mixture. However, this large-scale process presents significant safety issues associated with the transport of bulk H2O2. Moreover, the AO process can hardly be considered ail environmentally friendly method. In view of this, more economical and environmentally cleaner routes have been explored for the production of H2O2. The liquid-phase catalytic direct synthesis of H2O2 from H-2 and O-2 offers an attractive green technology for small-scale/onsite production of H2O2. However, the direct synthesis process suffers from two major drawbacks: (i) potential hazards associated with H-2/O-2 mixtures and (ii) poor selectivity for H2O2 because the catalysts used for H2O2 synthesis are also active for its decomposition and hydrogenation to water as well as for H-2 combustion. These serious issues and the recent developments in the direct H2O2 synthesis are discussed in this review. The roles of protons (H+) and halide ions in promoting the H2O2 selectivity are also examined in detail. (C) 2008 Elsevier B.V. All rights reserved