A320 returned to departure airport when the Yellow Hydraulic System quantity fell to zero.

Narrative

Just before reaching our cruising altitude we had an ECAM stating that we had lost our yellow hydraulic system. We followed QRH procedures with the First Officer the pilot flying; I contacted Dispatch and told them of our situation. We agreed that the best course of action was to declare an emergency and return to our departure airport for an over-weight landing. I then informed ATC of our situation and got turned around and headed back to our departure airport. Then; I informed the flight attendants of the situation and that we would be going back for a normal landing. I also made a PA and told the passengers the same thing. At that time our departure airport was using a south operation. I requested and received runway 36C. The winds were calm and there was weather from the west around to the northeast about 10 to 15 miles away. On short final we smelled what we thought could have been hydraulic fluid. After clearing the runway we had the emergency personnel check for any more leaking fluid before taxiing to the gate. First Officer and I worked very well as a team. One thing that I thought I could have done better was to restate that it was going to be a normal landing to both the passengers and the flight attendants.