  We explicitly find an equation and a projective embedding of the Kummer
surface associated to the Jacobian of a curve of genus 2 given by an equation
of the form y^2 + h(x)y = f(x) over an arbitrary ground field as well as
several maps that can be used to perform arithmetic on it. This extends earlier
work by Flynn and has applications, for instance, in computations of canonical
heights for genus 2 Jacobians and in cryptography.
