This paper investigates whether non-linear gravitational instability can account for the clustering of galaxies on large and small scales, and for the evolution of clustering with epoch. The local clustering spectrum is accurately established, and bias is not a great source of uncertainty: the real-space power spectra of optical and IRAS galaxies show only a weak scale-dependent relative bias of b ≃ 1.15 on large scales, increasing to b ≃ 1.5 on the smallest scales. Comparison with results in redshift space favours a relatively small distortion parameter βopt ≣ Ω0.6/bopt ≣ 0.4.