  In this paper, we consider solutions to the following nonlinear Schr\"odinger
equation with competing Hartree-type nonlinearities, $$ -\Delta u + \lambda
u=\left(|x|^{-\gamma_1} \ast |u|^2\right) u - \left(|x|^{-\gamma_2} \ast
|u|^2\right) u\quad \mbox{in} \,\, \R^N, $$ under the $L^2$-norm constraint $$
\int_{\R^N} |u|^2 \, dx=c>0, $$ where $N \geq 1$, $0<\gamma_2 < \gamma_1
<\min\{N, 4\}$ and $\lambda \in \R$ appearing as Lagrange multiplier is
unknown. First we establish the existence of ground states in the mass
subcritical, critical and supercritical cases. Then we consider the
well-posedness and dynamical behaviors of solutions to the Cauchy problem for
the associated time-dependent equations.
