A complex control system constructed from biochemically-based logic circuitry governs cell's responses to external signals and management of their internal operations. In many of the critical reactions of this circuitry, particularly the genetic mechanisms of gene expression, the concentration of participating molecules is very low. This leads to stochastic variation in reaction rates in the circuits. The result is uncertainty in timing of decisions and even, in some cases, to uncertainty in phenotype outcomes. We will discuss the physical origins of this noise, the consequences of the noise in human and bacterial genetics, and some of the mechanisms used to achieve high reliability necessary for creation of complex organisms in spite of the noise.