This review summarizes the field's major findings related to the characterization of polyomavirus structures and to the characterization of virus receptors and mechanisms of host cell invasion. The four members of the family that have received the most attention in this regard are the mouse polyomavirus (mPyV), the monkey polyomavirus SV40, and the two human polyomaviruses, JCV and BKV. The structures of both the mPyV and SV40 alone and in complex with receptor fragments have been solved to high resolution. The majority of polyomaviruses recognize terminal sialic acid in either an alpha2,3 linkage or an alpha2,6 linkage to the underlying galactose. Studies on virus structure, receptor utilization and mechanisms of entry have led to new insights into how these viruses interact in an active way with cells to ensure the nuclear delivery and expression of their genomes. Critical work on virus entry has led to the discovery of a pH neutral endocytic compartment that accepts cargo from caveolae and to novel roles for endoplasmic reticulum (ER) associated factors in virus uncoating and penetration of ER membranes. This review will summarize the major findings and compare and contrast the mechanisms used by these viruses to infect cells.