In this paper, phenomena of enhanced nucleation and crystallization of biological and inorganic materials on porous silicon (PS) are reviewed and explained using a microscopic approach accounting for the size and shape of individual pores. The facilitation of crystallization on PS is explained by the decrease of the potential barrier of nucleation, related to the decrease of the critical nucleus volume at heterogeneous nucleation in pores. For fractal surfaces, this decrease results in spontaneous solidification under minimal total supersaturation due to the wide distribution of pore sizes. (C) 2011 Elsevier B.V. All rights reserved.