Forensic engineering within civil engineering involves the investigation of failures of construction facilities and the built environment. While collapses are the most spectacular and potentially lethal type of failures - particularly when caused by criminal acts such as terrorism and arson - the discipline also includes investigation of failures in serviceability and performance, both during and after construction. The key to forensic engineering is that the investigation practice and procedure should be sufficiently robust to stand up to rigorous scrutiny. It needs to embrace examination of a range of technical and organisational factors that may have contributed to a failure, especially where it results in claims and litigation. There is also a wider benefit in that the outcomes of forensic investigation and assessment can increase the sustainability of infrastructures by prolonging its use. The papers in this special issue report on the forensic investigation of everything from collapse to cracks in a diverse range of structures from around the world, with causes including blast, fire, storm, flood, erosion and corrosion.