In the nucleus of higher organisms the DNA is organized by histone proteins into a nucleoprotein complex termed chromatin. This packing controls DNA accessibility and is therefore an important factor for the control of gene expression.We developed a new coarse-grained computer model to represent different types of chromatin fibers. Based on model structures at atomic resolution, the common two-angle nucleosome geometry was enhanced by four additional angles. The nucleosomes are modeled as spherocylinders described by an S-functions expansion and are connected by cylindrical DNA segments. Harmonic potentials for stretching, bending, and torsion represent the elastic properties of the DNA. The negative charge of the DNA is described by a Debye-Huckel-approximation. This model was used to investigate the influence of the local nucleosome geometry and the internucleosomal interaction on the chromatin fiber conformation by Monte Carlo (MC) simulations [1,2]. Three fiber types derived from experimental data of native and reconstituted chromatin were systematically analyzed. For all investigated fiber types, the simulations revealed the large impact of the nucleosome repeat length on the stability of the fiber formation. A model was proposed, in which changes of the chromatin fiber conformation induced by linker histone H1 binding as predicted from high resolution model structures are reproduced by relatively small changes of the local nucleosome geometry. Furthermore, key factors for the control of the compaction and higher order folding of the chromatin fiber were identified. We have further developed this approach and are applying it to the analysis of the conformational space of the chromatin fiber, fiber force spectroscopy experiments and atomic force microscopy imaging of chromatin fibers.[1] Stehr, R., N. Kepper, K. Rippe, and G. Wedemann. Biophys. J. 95:3677 (2008).[2] Kepper, N., D. Foethke, R. Stehr, G. Wedemann, and K. Rippe. Biophys. J. 95:3692 (2008).