Without the trusted and capable packages Mosflm, CCP4, Scala and XDS it would clearly be impossible to develop xia2. The author would therefore like to thank Andrew Leslie, Harry Powell, Phil Evans, Wolfgang Kabsch and Kay Diederichs for their assistance in using their programs and modi- fications they have made. In addition, more recent developments such as DIALS 1 , Pointless 2 and CCTBX 3 have made the development of xia2 much more straightforward and the end product more reliable. The author would therefore like to additionally thank Nick Sauter and Ralf Grosse-Kunstleve for their help. Development of a package such as this is impossible without test data, for which the author would like to thank numerous users, particularly the Joint Center for Structural Genomics, for publishing the majority of their raw diffraction data. During the course of xia2 development the project has been supported by the UK BBSRC through the e-HTPX project, the EU Framework 6 through the BioXHit project and most recently by Diamond Light Source. The software itself is open source, distributed under a BSD license, but relies on the user having correctly configured and licenced the necessary data analysis software, the details of which will be discussed shortly.