We present an integrated, quantitative picture of urban dynamics showing that many properties of cities are power-law functions of population size with universal scaling exponents β . Quantities reflecting wealth creation and innovation have β ≈ 1.2 > 1 (increasing returns), while infrastructural ones display β ≈ 0.8 < 1 (economies of scale). This suggests that generic properties of cities are derivable from underlying principles common to all urban systems. We predict that the pace of life increases, in quantitative agreement with data, and derive a growth equation showing how major innovation cycles must be generated at a continually accelerating rate to sustain growth and avoid stagnation or collapse.