  Quantum impurity solvers have a broad range of applications in theoretical
studies of strongly correlated electron systems. Especially, they play a key
role in dynamical mean-field theory calculations of correlated lattice models
and realistic materials. Therefore, the development and implementation of
efficient quantum impurity solvers is an important task. In this paper, we
present an open source interacting quantum impurity solver toolkit (dubbed
$i$QIST). This package contains several highly optimized quantum impurity
solvers which are based on the hybridization expansion continuous-time quantum
Monte Carlo algorithm, as well as some essential pre- and post-processing
tools. We first introduce the basic principle of continuous-time quantum Monte
Carlo algorithm and then discuss the implementation details and optimization
strategies. The software framework, major features, and installation procedure
for $i$QIST are also explained. Finally, several simple tutorials are presented
in order to demonstrate the usage and power of $i$QIST.
