Bifurcations of the periodic stationary solutions of nonlinear time-periodic time-delay dynamical systems are analyzed. The solution operator of the governing nonlinear delay-differential equation is approximated by a sequence of nonlinear maps via semidiscretization. The subsequent nonlinear maps are combined to a single resultant nonlinear map that describes the evolution over the time period. Fold, flip, and Neimark-Sacker bifurcations related to the fixed point of this map are analyzed via center manifold reduction and normal form theorems. The analysis unfolds the approximate stability properties and bifurcations of the stationary solution of the delay-differential equation and, at the same time, allows the approximate computation of the arising period-1, period-2, and quasi-periodic solution branches. The method is demonstrated for the delayed Mathieu-Duffing equation, and the results are verified by numerical continuation. 57 58 MOLNAR ET AL.the nonlinear time-periodic DDE using a nonlinear map that describes the evolution over the time period. The fixed point of this map corresponds to the stationary solution of the original DDE. Fold, flip, and Neimark-Sacker bifurcations of the fixed point are associated with cyclic fold, period doubling, and secondary Hopf bifurcations of the stationary solution, respectively, which may give rise to period-1, period-2, and quasi-periodic solutions. We determine the stability of these solutions by analyzing the fixed point of the corresponding nonlinear map and calculating its critical normal form coefficients. Via these coefficients, we use analytical formulas to obtain the approximate amplitude of the bifurcating solutions as a function of the bifurcation parameter. Therefore, as opposed to Knut, this method does not require the point-by-point continuation of the arising solutions; however, the results are accurate in the vicinity of the bifurcation point only, and secondary bifurcations cannot be detected.The first step of the analysis is to discretize the solution operator of the nonlinear time-periodic DDE. Several techniques exist for discretizing DDEs (see the works of Krauskopf et al, 9 Loiseau et al, 10 and Breda et al 11 where some relevant approaches are collected). The most popular and most efficient numerical methods include the pseudospectral collocation, 12,13 the Chebyshev spectral continuous-time approximation, 14 the spectral element method, 15 the spectral Legendre tau method, 16 and the pseudospectral tau method. 17 In what follows, we use the semidiscretization technique 18 to discretize the solution operator of the DDE. This method formulates a sequence of nonlinear maps that approximate the dynamics over the time period. Note that the approach of this paper is not restricted to semidiscretization; it supports other discretization techniques as well, as long as the solution operator is approximated by a (sequence of) nonlinear map(s) over the time period.We show an algorithm to build a single resultant map from the sequence of nonlinear maps that i...