This document is a paper from the 5th National Symposium on Biosafety that includes the associated PowerPoint slides from the presentation given at the symposium. The document is based upon the CDC/NIH 3rd edition of Biosafety in Microbiological and Biomedical Laboratories. From the earliest days of microbiological research, laboratorians have recognized that acquiring infections from the agents they manipulated was a recognized occupational hazard. The most commonly-acquired lab infections were caused by bacterial agents; as microbiologists learned to culture animal viruses, they also found ways to become infected with these agents. From the literature reviews of Sulkin and Pike, we also learned that a significant number of these infections were fatal and that most infections were of unknown origin. Guidelines evolved as a means of protecting microbiological workers based on these data and an understanding of the risks associated with various manipulations of many agents transmissible by different routes. These guidelines work from the premise that safe work sites result from a combination of engineering controls, management policies, work practices and procedures, and, occasionally, medical interventions. The different biosafety levels developed for microbiological and biomedical laboratories provide increasing levels of personnel and environmental protection. Upper level management must set the general tone that safety is a high priority at their institute. Though this is often expressed in broad policy statements, it must be supported by resource allocation decisions: financial, personnel staffing, training, a safety performance reward structure, etc. For each biosafety level there are also specific supervisory qualifications as assurance that the laboratorians are provided appropriate role models and knowledgeable mentors. Crucial to safe working conditions are the various types of specialized equipment available to serve as primary barriers between the microorganism and the laboratorian.