Physical Conditions in the ISM and the Star Formation-H2 Connection

Stunning leaps in data quality over the last decade have revealed important variations in how 
stars form out of gas across the universe. With the next generation of telescopes and surveys, 
it is now becoming possible to move beyond bulk correlations to ask: how do conditions within 
the molecular gas drive the ability of that gas to form stars and how do these conditions depend 
on galactic environment? I will review several aspects of this topic including the role of dense 
gas, as traced by high effective density molecules like HCN and HCO+, and the link between 
the properties of individual molecular clouds and star formation. I will highlight results from the 
IRAM large program PAWS, the pilot for the new EMPIRE large program, and a new survey of 
HCN and HCO+ in the disks of normal spiral galaxies. I will also discuss the connection to 
recent Milky Way results and how observations with new facilities like ALMA and MUSE can 
help us take the next step in understanding the physics of gas and star formation in galaxies.