A theoretical model is proposed for hologram recording in photoformers (polymer aggregates with polymerization-diffusion mechanism of refractive index modulation and/or absorption coefficient modulation). The main attention is concentrated on binary (bi-component) photoformers. The latter are a mixture of monomers (or monomer and neutral component) with different refractive indexes n1≠ n2 or absorption coefficients α1≠ α2. The importance of nonlinear diffusion under inhomogeneous photopolymerization is underlined. The generalization of the Fick's law for diffusion in the systems with the phase transformations of the mixture components is discussed. The holographic technique is successfully used for experimental evaluation of some photopolymer parameters: polymer chain termination order, diffusivity, etc.