Do I need an ISRC Code for my album or a UPC code?

The retailers, online distributors, and the Billboard Charts (SoundScan) set forth these requirements:
You need ISRC codes for each track of your album. However, the album itself requires a UPC code. In fact, if you plan to sell your album as a digital download AND as a physical audio CD then you need 2 UPC codes: one for the digital album download and a second one for the physical audio CD. This is the only way that performance on your individual songs can be tracked versus sales of the physical audio CD versus downloads of the complete digital album.

What about Singles?

For singles, you definitely need an ISRC code for the track. It is highly recommended that you also get a UPC code for singles because a UPC code is required on a single by: iTunes
Nielsen SoundScan to participate in the Billboard Charts
Retailers, if you plan to release the single as a physical CD
Even some of the aggregators, streaming sites, and download sites