Pulsed laser ablated boron atoms were reacted with ammonia during condensation at 10 K with excess argon. Reaction products were identified from matrix infrared spectra by isotopic substitution (B-10, B-11 (NH3)-N-15, ND3), photolysis behavior, and comparison to ab initio calculated frequencies. The major primary reaction is insertion to form the [HBNH2]* intermediate, which either dissociates to BH and NH2, eliminates H or H-2 to give products, or relaxes in the matrix. The major primary product is iminoborane, HBNH, a reactive molecule isoelectronic with acetylene, and a minor primary product is the photosensitive BNH radical. A second boron atom can react with primary products, and the major secondary reaction products are cyclic B2N radical and linear BNBH. These studies show that atomic boron reacts readily with ammonia.