Dynamical systems with a coupled cell network structure can display synchronous solutions, spectral degeneracies, and anomalous bifurcation behavior. We explain these phenomena here for homogeneous networks by showing that every homogeneous network dynamical system admits a semigroup of hidden symmetries. The synchronous solutions lie in the symmetry spaces of this semigroup and the spectral degeneracies of the network are determined by its indecomposable representations. Under a condition on the semigroup representation, we prove that a one-parameter synchrony breaking steady state bifurcation in a coupled cell network must generically occur along an absolutely indecomposable subrepresentation. We conclude with a classification of generic oneparameter bifurcations in monoid networks with two or three cells. © 2014 Society for Industrial and Applied Mathematics.