. The goal of these notes is to give a short introduction to Fukaya categories and some of their applications. The first half of the text is devoted to a brief review of Lagrangian Floer (co)homology and product structures. Then we introduce the Fukaya category (informally and without a lot of the necessary technical detail), and briefly discuss algebraic concepts such as exact triangles and generators. Finally, we mention wrapped Fukaya categories and outline a few applications to symplectic topology, mirror symmetry and low-dimensional topology.These notes are in no way a comprehensive text on the subject; however we hope that they will provide a useful introduction to Paul Seidel's book [40] and other texts on Floer homology, Fukaya categories, and their applications. We assume that the reader is generally familiar with the basics of symplectic geometry, and some prior exposure to pseudo-holomorphic curves is also helpful; the reader is referred to [28,29] for background material.Acknowledgements. The author wishes to thank the organizers of the Nantes Trimester on Contact and Symplectic Topology for the pleasant atmosphere at the Summer School, and Ailsa Keating for providing a copy of the excellent notes she took during the lectures. Much of the material presented here I initially learned from Paul Seidel and Mohammed Abouzaid, whom I thank for their superbly written papers and their patient explanations. Finally, the author was partially supported by an NSF grant (DMS-1007177).1. Lagrangian Floer (co)homology 1.1. Motivation. Lagrangian Floer homology was introduced by Floer in the late 1980s in order to study the intersection properties of compact Lagrangian submanifolds in symplectic manifolds and prove an important case of Arnold's conjecture concerning intersections between Hamiltonian isotopic Lagrangian submanifolds [12].Specifically, let (M, ω) be a symplectic manifold (compact, or satisfying a "bounded geometry" assumption), and let L be a compact Lagrangian submanifold of M . Let ψ ∈ Ham(M, ω) be a Hamiltonian diffeomorphism. (Recall that a time-dependentThe author was partially supported by NSF grant DMS-1007177. Note that, by Stokes' theorem, since ω |L = 0, the symplectic area of a disc with boundary on L only depends on its class in the relative homotopy group π 2 (M, L).The bound given by Theorem 1.1 is stronger than what one could expect from purely topological considerations. The assumptions that the diffeomorphism ψ is Hamiltonian, and that L does not bound discs of positive symplectic area, are both essential (though the latter can be slightly relaxed in various ways). Example 1.2. Consider the cylinder M = R × S 1 , with the standard area form, and a simple closed curve L that goes around the cylinder once: then ψ(L) is also a simple closed curve going around the cylinder once, and the assumption that ψ ∈ Ham(M ) means that the total signed area of the 2-chain bounded by L and ψ(L) is zero. It is then an elementary fact that |ψ(L) ∩ L| ≥ 2, as claimed by Theorem 1.1; see Figure 1 left. O...