The infrastructures on which our society depends not only can have failures propagating within the infrastructure but also between infrastructures. For example, Cleveland lost its water supply during the August 2003 blackout of the Northeastern USA and the loss of the twin towers in New York in September 2001 impacted both subway transport and communications. Multiple dependent and cascading failures occur when humans make honest errors in operating infrastructures. Recovering from failures spanning multiple infrastructure is complicated and expensive. While these interdependencies are becoming increasingly recognized and described qualitatively, this session explores methods to quantify the complex interactions of failures within and between infrastructures. Advances in modeling and analyzing these interactions are needed.