Strong dynamics, minimal flavor and R_b

We discuss how models of electroweak symmetry breaking based on strong dynamics lead to observable contributions to the Z-boson decay width to bbbar pairs even in the absence of any extended sector responsible for dynamical generation of the masses of the Standard Model matter fields. These contributions are due to composite vector mesons mixing with the Standard Model electroweak gauge fields and lead to stringent constraints on models of this type. Constraints from unitarity of WW-scattering are also considered.