Alkanes are among the most abundant and unreactive of all organic compounds. Industrial use of these resources often relies upon free-radical activation of carbon-hydrogen bonds, often at high temperatures, thereby limiting the selectivities that can be achieved in any functionalization reaction. Consequently, the selective activation of C-H bonds by homogeneous transition-metal compounds has been a topic that has been of great interest to the organometallic community for many years. In this Account, mechanistic studies with a series of homogeneous rhodium organometallic complexes are summarized that provide for the first time a comparative evaluation of the relative equilibrium constants and rates of reaction for both alkane and arene hydrocarbon activation.