What Happens If The House & The Senate Don't Agree On A Bill?

In instances where each chamber passes a bill similar to each other but have specific differences, generally the bill goes to "conference committee".  This is a committee appointed by the leadership in each chamber and charged with the responsibility to negotiate a common ground on the bill so that it is returned to both chambers in the exact same format and voted on again.  The committee has members of both parties so that the recommendation of the conference committee is likely to be adopted by both chambers.  If a bill is passed in one chamber and the other chamber does not agree with it and votes it down it very well could be dead, unless amendments are made to satisfy the opposing chamber.