For more than 20 years there has been confusion concerning Class II biological safety cabinet (BSC) terminology. This has lead to problems in under- standing just what the types of Class II BSCs are, and how they should be installed and used. The changes in the NSF/ANSI Standard 49 - 2002 are intended to resolve many of these issues. A good way to grasp all of this is to become familiar with the evolution of Class II BSC terminology. Achieving this should enable us to properly interpret the relevant literature which contains a myriad of terms that have been applied to Class II BSCs. Additionally, it will make it possible for us to understand each other when we discuss BSCs.