The cause of the “Y2K bug” was relatively simple: to save on limited memory space, engineers initially coded computer systems to recognize years as two-digit rather than four-digit numbers. For example, 99 instead of 1999. But what would happen when the calendar rolled over to January 1, 2000? Would computers misread the year as 1900? How might that error disrupt software and technology dependent upon internal clocks and calendars—particularly within critical sectors like utility services, healthcare, telecommunications, transportation, banking, and emergency preparedness? Would the entire global computing infrastructure collapse? The US Department of Commerce estimated that the United States spent roughly $100 billion preparing for Y2K. Global expenditures topped $300 billion. With few major failures reported as a new millennium dawned, those involved declared victory for collective preventative action while skeptics challenged the need for widespread alarm. Risk severity remains difficult to determine, but experts credit Y2K readiness for how it improved computing systems during later catastrophes, such as the 9/11 terrorist attacks, and transformed the global tech industry.