Testing Extended Technicolor With R_b

We review the connection between $m_t$ and the $Zb\bar b$ vertex in ETC models and demonstrate the power of the resulting experimental constraint on models with weak-singlet ETC bosons. Some efforts to bring ETC models into agreement with experimental data on the $Zb\bar b$ vertex are mentioned, and the most promising one (non-commuting ETC) is discussed in detail.