Selling to the federal government is not ordinary commercial contracting with extra paperwork; it is a distinct legal system in which the buyer writes the rules, keeps sovereign powers it can exercise mid-performance, and enforces the bargain with criminal and quasi-criminal tools no private customer possesses. This UpLaw guide maps that system end to end: the Federal Acquisition Regulation and its agency supplements, the competition mandate of the Competition in Contracting Act and the seven narrow exceptions to it, the contracting methods (sealed bidding, negotiated procurement under FAR Part 15, commercial products under Part 12, simplified acquisitions, GSA schedules, and IDIQ task-order competition), the contract types and how each allocates risk, responsibility determinations and organizational conflicts of interest, best-value tradeoff versus lowest-price technically acceptable evaluation, and the clauses that make a federal contract structurally different from a commercial one. It then works through the hard edges: the Christian doctrine, which reads mandatory clauses into a contract that omits them; FAR Part 31 cost principles and allowability; the Truthful Cost or Pricing Data statute and defective-pricing exposure; constructive changes and requests for equitable adjustment; claims, contracting-officer final decisions, and appeals to the boards or the Court of Federal Claims; terminations for convenience and default; bid protests at the agency, GAO, and the Court of Federal Claims; and the False Claims Act, mandatory disclosure, and suspension and debarment. A running hypothetical follows a first-time software vendor from proposal through a task order gone sideways, and the guide flags the thresholds and executive-branch policies that change often enough that any figure must be verified against the current FAR before you rely on it.