Formation of a planetary-scale impact crater hundreds of meters to hundreds of kilometers in diameter involves the interplay of multiphase processes occurring over size- and time-scales that range over many orders of magnitude. To further complicate matters, a hypervelocity impact into geologic materials has never been observed at greater than laboratory scales. Understanding the formation process clearly is a very complicated problem that requires a highly interdisciplinary approach. Significant work has been done recently in several key areas of impact studies, but in many respects, there is a “disconnect” among groups employing different approaches. This pertains, in particular, to modeling versus observations.