\title{Mackey functors and sharpness for fusion systems} \author{Antonio D\'iaz} \address{Departamento de \'Algebra, Geometr\'ia y Topolog\'ia, Universidad de M\'alaga, Apdo correos 59, 29080 M\'alaga, Spain} \author{Sejong Park} \address{School of Mathematics, Statistics and Applied Mathematics, National University of Ireland, Galway, University Road, Galway, Ireland} \thanks{\rm The first author is supported by MICINN grant RYC-2010-05663 and partially supported by FEDER-MCI grant MTM2010-18089 and Junta de Andaluc{\'\i}a grant FQM-213.} \begin{abstract} We develop the fundamentals of Mackey functors in the setup of fusion systems including an acyclicity condition as well as a parametrization and an explicit description of simple Mackey functors. Using this machinery we extend Dwyer's sharpness results to exotic fusion systems $\CF$ on a finite $p$-group $S$ with an abelian subgroup of index $p$. \end{abstract} To appear in Homology, Homotopy and Applications