The complex Zr(9-BBN)(4) [9-BBN = (mu-H)(2)BC8H14] has been synthesized via the reaction of K(9-BBN) with ZrCl4 in diethyl ether. The structure of the title compound has been determined by X-ray and neutron single-crystal diffraction techniques. Each 9-BBN ligand is coordinated to the Zr atom via two B-H-Zr bridges, and these metalligand bonding interactions are further augmented by three prominent C-H---Zr agostic interactions. Average molecular parameters derived from the neutron analysis: Zr-H = 2.051(8) angstrom, B-H = 1.286(7) angstrom, Zr---B = 2.409(6) angstrom, Zr-H-B = 87.7(4)degrees, H-Zr-H = 58.9(3)degrees. The Zr---H distances corresponding to the three C-H... Zr agostic interactions are 2.424(7), 2.663(8), and 2.551(7) angstrom. The fourth potential C-H---Zr interaction has a Zr---H distance [3.146(7) angstrom] that is too long to be considered in the agostic range. Single-crystal X-ray diffraction data were collected on an Enraf-Nonius Kappa CCD diffraction system, and neutron diffraction data were collected on the quasi-Laue diffractometer VIVALDI at the Institut Laue-Langevin; the final agreement factor for the neutron analysis is 6.52% for 2557 reflections with l > 2 sigma(l).