Obstructions to planarity of contact 3-manifolds

24 pages, 8 figures; major revision: we added new statements, and improved the exposition of the old ones. Comments are welcome!International audienceWe prove that if a contact 3-manifold admits an open book decomposition of genus 0, a certain intersection pattern cannot appear in the homology of any of its symplectic fillings, and morever, fillings cannot contain certain symplectic surfaces. Applying these obstructions to canonical contact structures on links of normal surface singularities, we show that links of isolated singularities of surfaces in the complex 3-space are planar only in the case of $A_n$-singularities, and in general characterize completely planar links of normal surface singularities (in terms of their resolution graphs). We also establish non-planarity of tight contact structures on certain small Seifert fibered L-spaces and of contact structures compatible with open books given by a boundary multi-twist on a page of positive genus. Additionally, we prove that every finitely presented group is the fundamental group of a Leschetz fibration with planar fibers