This is a Special Issue with 14 papers that are all concerned with the testing of software and systems. I am very grateful to the guest editors, Husnu Yenigun, Nina Yevtushenko, and Ana Rosa Cavalli, for all their hard work in producing an excellent set of papers on this topic. They have also provided a very helpful introduction to this issue to help you identify those papers of particular interest.

Please email me at rachel.harrison@brookes.ac.uk if you have any comments on this issue.