During mRNA translation, the genetic information stored in mRNA is translated into a protein sequence. It is imperative that the genetic information is translated with high precision. Surprisingly, however, recent experimental evidence has demonstrated that translation can be highly heterogeneous, even among different mRNA molecules derived from a single gene in an individual cell; multiple different polypeptides can be produced from a single mRNA molecule and the rate of translation can vary in both space and time. However, whether translational heterogeneity serves an important cellular function, or rather predominantly represents gene expression 'noise' remains an open question. In this review, we discuss the molecular basis and potential functions of such translational heterogeneity.