This was one of my textbooks for my metadata class this semester. If you work in a library, you need to be familiar with MARC21, in my opinion. The level to which you should be familiar obviously varies per position. For example, I only download the MARC records. However, I can view them and anyone with access to the bibliographic records can view them. So a basic understanding of MARC21 helps the library worker better understand his or her position. I now better understand what I'm downloading and how it is structured. This book gives a great walk-through to people who are new to and/or know the basics of MARC records. It is easy to read and gives many examples that make it even easier to learn. The author talks to you in laymen's terms while teaching you metadata and MARC record terms. I would suggest anyone who views MARC records at all to at least know the basics. This is a great book to start for that!