In this column, I summarize the 12 worst of the most common requirements engineering problems I have observed over many years working on and with real projects as a requirements engineer, consultant, trainer, and evaluator. I also list the negative consequences of these problems, and most importantly suggest some industry best practices that can help you avoid these problems, or at least fix them once they have raised their ugly heads. Although there is nothing really new here, these problems are well worth revisiting because they are still far too common, probably because the associated industry best practices are still far from being widely put into practice.