A contract modification is any written change to a contract after award, executed by the contracting officer under FAR Part 43. Modifications fall into two procedural categories. Bilateral modifications — supplemental agreements — require both parties to sign Standard Form 30. Unilateral modifications are issued by the CO alone under specific contractual authority, most commonly to exercise priced options, make administrative changes, or issue change orders under the Changes clause. Only the CO can authorize a modification; verbal direction from a COR does not bind the government.
The substantive types of modifications matter as much as the procedure. Change orders direct the contractor to perform work outside the original scope under the Changes clause and entitle the contractor to an equitable adjustment to price and schedule. Administrative changes update non-substantive items — billing addresses, accounting strings, points of contact. Supplemental agreements cover anything requiring mutual consent: scope additions, cost overruns within ceiling authority, novations after corporate restructuring. Option exercises are unilateral acts the government can take within the option exercise window. Out-of-scope modifications can be challenged as cardinal changes — modifications so substantial they fall outside the Changes clause and require resolicitation.
For small contractors, modification discipline is a margin protection issue. Performing work directed by program-office staff without a written modification creates uncompensated effort. The reliable rule is to document any direction from the COR, escalate to the CO, and refuse to perform out-of-scope work without a written change order on file.