  We present the SPEX software package for modeling and fitting X-ray spectra.
Our group has developed spectral models, atomic data and code for X-ray
applications since the 1970's. Since the 1990's these are further developed in
the public SPEX package. In the last decades, X-ray spectroscopy has been
revolutionized by the high-resolution grating spectrometers aboard XMM-Newton
and Chandra. Currently, new high-resolution detectors aboard the Hitomi
mission, and future missions, like XRISM and Athena, will provide another major
step forward in spectral resolution. This poses challenges for us to increase
the atomic database substantially, while keeping model calculation times short.
In this paper, we summarize our efforts to prepare the SPEX package for the
next generation of X-ray observatories.
