In this work the nonlinear in-plane behavior of circular arches with hollow circular cross-section is investigated. The influence of a number of design parameters, such as the boundary conditions, the rise-to-span ratio, and the included angle on the strength is presented. Moreover, the effect of other behavior factors, such as the geometrical and material nonlinearities and the initial imperfections, is investigated. A criterion for the prediction of the type of nonlinear behavior of arches is given, and a formula for the determination of the nonlinear buckling load is proposed. It is found that the effect of initial imperfections on the strength depends largely on the arch slenderness and the imperfection magnitude in the case of shallow arches. When arches are deep this dependence becomes less significant. The effect of geometrical nonlinearity depends significantly on the shallowness and the slenderness of the arches. Stocky arches are less influenced by the rise-to-span ratio than slender ones. The effect of boundary conditions depends significantly on the shallowness of arches and the arch slenderness. The reduction of strength is larger in slender arches than in stocky ones.