In recent years there have been several bridge collapses in the United Kingdom and Republic of Ireland that have been caused by scour. Towns in the north west of England have been cut off and loss of life occurred. Major railway lines have been closed for extended periods. Although scour is basically the removal of bed material due to flowing water, it has a number of different causes and takes different forms. The paper describes the different forms of scour and looks at a number of case studies to illustrate the different ways in which scour has caused structures to collapse or require protection. The case studies are of railway bridges and are drawn from official investigation reports and underwater examinations carried out by the author. The paper concludes by illustrating ways in which failures due to scour could be avoided by the employment of good bridge management systems.