This paper reports the recent development and applications of conductive borondoped ultrananocrystalline diamond (BD-UNCD). The authors have determined that BD-UNCD can be synthesized with an H-rich gaseous chemistry and a high CH 4 /H 2 ratio, which is opposite to previously reported methods with Ar-rich or H-rich gas compositions but utilizing very low CH 4 /H 2 ratio. The BD-UNCD has a resistivity as low as 0.01 ohm·cm, with low roughness (down to several nm) and a wide deposition temperature range (450-850¼C).The properties of this BD-UNCD were studied systematically using resistivity characterization, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and roughness measurements. Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy confirms that up to 97% of the UNCD is deposited as sp3 carbon.These series of measurements also reveal additional unique properties for this material, such as an ÒMÓ shape Raman signature, line-granular nano-cluster texture and high C-H bond surface content. A hypothesis is provided to explain why this new deposition strategy, with H-rich/Ar-free gas chemistry and CH 4 /H 2 ratio, is able to produce high sp3-content and/or 2 heavily doped UNCD. In addition, a few emerging applications for BD-UNCD in the field of atomic force microscopy, electrochemistry and biosensing are reviewed here.