Antenna current optimization is used to determine optimal current distributions in the design region. The currents provide understanding, physical bounds, and figures of merits for antenna designs. The antenna current optimization problem is formulated as a convex optimization problem. The Q-factor is defined as the quotient between the stored and dissipated energies and is used to quantify the bandwidth performance of resonant structures. An approach based on a state-space model of the antenna input impedance proposed. The state-space model describes the internal states of the system and models the states that store the energy. The state-space model is determined from the impedance matrix of the electric field integral equation. In this presentation, antenna current optimization and stored electromagnetic energy expressions are reviewed. Numerical results for maximization of the gain to Q-factor quotient and minimization of the Q-factor for prescribed radiated fields are presented.