Through the use of Pd-2(dba)(3)/P(t-Bu)(3) as a catalyst, a wide range of aryl and vinyl halides, including chlorides, undergo Suzuki cross-coupling with arylboronic acids in very good yield, typically at room temperature; through use of Pd(OAc)(2)/PCy3, a diverse array of aryl and vinyl triflates react cleanly at room temperature. Together, these two catalyst systems cover a broad spectrum of commonly encountered substrates for Suzuki couplings. Furthermore, they display novel reactivity patterns, such as the selective cross-coupling by Pd-2(dba)(3)/P(t-Bu)(3) of an aryl chloride in preference to an aryl triflate, and they can be used at low lending, even for reactions of aryl chlorides. Preliminary mechanistic work indicates that a palladium monophosphine complex is the active catalyst in the cross-coupling of aryl halides.