This site does not focus on federal acquisition, but because the FAR is frequently referenced when discussing assistance issues — sometimes appropriately, sometimes not — it seems to make sense to at least provide a few comments on it.
Find the FAR on line at these sites:
The FAR governs federal acquisitions (procurement contracts). Thus, unless the terms and conditions of an assistance award agreement specifically reference the FAR, FAR rules do not govern assistance awards. The OMB's uniform guidance at 2 CFR 200 provides all the rules needed to govern assistance awards. So don't get bogged down in the FAR unless you have to.
One important circumstance where the FAR may apply in the assistance environment is when an assistance award is made to a commercial entity. In such cases, most federal awarding agencies stipulate that the FAR's cost principles (found at FAR Part 31) apply to commercial recipients of assistance awards. But this is not as big a deal as it may seem. Careful review of the FAR cost principles reveals that they are largely identical to those of 2 CFR 200 Subpart E, with the significant differences appearing as extensions and amplifications of a few of the selected items of cost (48 CFR 31.205-1 - __.205-52, and 2 CFR 200.420 - __.475) where large and/or sophisticated commercial entities may require more refined accounting guidance.
EXCEPTION: Note that as of DEC 2014, USAID applies 2 CFR 200 Subpart E to commercial recipients of USAID assistance awards. See Notes on 2 CFR 700.