Many crystalline materials are known to exhibit creep at low temperatures (T < 0.3T (m)). Here, we review and analyze the phenomenological relationships that describe primary creep. The discussion focuses on the controversy as to whether power-law or logarithmic descriptions better describe the experimental database. We compile data from the literature as well as new copper data recently taken by the authors. Depending on the material, it appears that the logarithmic form can somewhat better describe creep behavior at low temperatures, while the power-law behavior manifests at intermediate temperatures. The basic mechanism(s) of low-temperature creep plasticity is examined, as well.