Driven-Dissipative Polariton Condensate — Exciton-polaritons (light-matter quasiparticles in microcavities) form a non-equilibrium condensate governed by the driven Gross-Pitaevskii equation: iℏ∂ψ/∂t = [−ℏ²∇²/2m + g|ψ|² − iκ/2]ψ + F. Unlike equilibrium BEC, here gain balances loss. Bistability occurs when the nonlinear resonance bends — the system can snap between low/high density branches. Vortices (phase windings of ±2π) are topological defects with quantized circulation.