The budget justification is a very important part of any proposal budget.  The justification explains in detail all of the proposed expenses shown in the proposed budget.  

Below is a link to a sample detailed budget justification:

UND Detailed Budget Justification - Sample

Below are links to templates for specific budget categories.  These templates may help you explain certain expenses within your budget justification:

Communications

Postage

Data Processing

Equipment

Food Purchases

Fringe Benefits

General

F&A (Indirect Costs)

Instructional

Memberships

Office Supplies

Pre-Proposal Verbage

Salary Overload

Supplies

Travel