This chapter identifies some of the major components and connotations of the risk concept. Risks are prominent on the public agenda, and risk abatement is a central component of a wide variety of human practices. A major difference in general usage between 'ignorance' and 'uncertainty' seems to be that 'uncertainty' refers to lack of knowledge that the individual is aware of, whereas 'ignorance' denotes lack of knowledge that she may or may not be aware of. And when scientific knowledge has been eliminated from our concept of risk, only ignorance and values remain. In fairness, it should be emphasized that today, probabilistic risk analysis (PRA) specialists are well aware of this. There are still analysts who maintain that the method can be used to "evaluate the riskiness of a technology" and to compare "the health impacts of competing technologies so a rational judgment can be made of their relative acceptability".